f. fx 0-10 10-20 20-30 30-40 40-50 50-60 60-70 5 15 25 35 45 55 65 3 2 5 8 4 6 2 15 30 125 280 180 330 130 N = 30 Σ fx =1090 (ii) Calculation of Arithmetic Mean by Short Cut Method : DailyExpenditure (in Rs.) Apart from the stuff given on this web page, if you need any other stuff in math, please use our google custom search here. Properties of average. Terms of Service 7. The mean will be displayed if the calculation is successful. Steps to be followed are, Prepare a table containing five columns; Write the class intervals in column 1 It is equal to the sum of all the values in the group of data divided by the total number of values. Direct method. Solution:. Here, the upper limit of one class is the lower limit of the next class. Divide by the . Geometric mean is also applied in computing financial indices as it is more reliable and a better measure than arithmetic mean. Relationship between Arithmetic Mean, Geometric Mean and Harmonic Mean: Relationship between arithmetic mean (AM), geometric mean (GM) and harmonic mean (HM) can be expressed as: Statistics, Central Tendency, Measures, Arithmetic Mean. This factor is taken into consideration by weighted arithmetic mean which takes into account the weights (importance) assigned to each and every value. Short-cut method 1. Otherwise, figure out the frequency of each variable and they are denoted by fiand the n… Calculate Arithmetic mean by direct, Assumed mean and step deviation methods for the following data. Uploader Agreement. Mean (or average) of observations, as we know, is the sum of the values of all the observations divided by the total number of observations. Arithmetic Method Calculation of Arithmetic Mean in Frequency Distribution. Use the formula (a) Direct Method: In direct method, the arithmetic mean is calculated by the following formula: The above formula shows that the sum of product of frequencies with their respective variables (Σfx) is to be divided by the sum of the frequencies (Σf) to derive arithmetic mean. Plagiarism Prevention 5. When weights are provided, the arithmetic mean is calculated using the following formula: Arithmetic mean is a widely used measure of central value due to the following advantages: 3. 5. Usage of geometric mean in the calculation of HDI decreases the level of substitutability between dimensions. Arithmetic mean formula Arithmetic mean for grouped data can be obtained in two methods which are, (i) Direct Method and (ii) Assumed Mean Method. Calculate the Arithmetic mean of the following data by direct method. 4. Take sum of to obtain . To clear the calculator and enter new data, press "Reset". If x 1 , x 2 ,… x n , are observations with respective frequencies f 1 , f 2 ,, . b> Median formulas: 1> Median for ungroup data: The method of calculating the mean taking deviations from the assumed mean is also called as the step deviation method. Content Guidelines 2. 40, 50, 55, 78, 58. Following is an example of individual series: In short-cut method, an arbitrary origin is taken and deviations are calculated from this arbitrary origin. Solution for b) Calculate the arithmetic using direct method and short-cut method mean of the following data: Marks 0-10 10-20 20-30 30-40 40-50 50-60 60-70… Harmonic mean is calculated as the average of the reciprocals of the values given. Arithmetic mean formula. Content Filtration 6. Replies. Direct method 2. Hence the required arithmetic mean for the given data is 45. Short cut method . Calculate the mean age of the students, Hence the required arithmetic mean for the given data is 15.45. The formula for the direct method is as follows: Mean= ∑fX/∑f Here, ∑fX= Summation of the product of values of items with their corresponding frequencies Also called the shift of origin method, this method is used when the calculation by the direct method becomes very tedious. Solving linear equations using elimination method, Solving linear equations using substitution method, Solving linear equations using cross multiplication method, Solving quadratic equations by quadratic formula, Solving quadratic equations by completing square, Nature of the roots of a quadratic equations, Sum and product of the roots of a quadratic equations, Complementary and supplementary worksheet, Complementary and supplementary word problems worksheet, Sum of the angles in a triangle is 180 degree worksheet, Special line segments in triangles worksheet, Proving trigonometric identities worksheet, Quadratic equations word problems worksheet, Distributive property of multiplication worksheet - I, Distributive property of multiplication worksheet - II, Writing and evaluating expressions worksheet, Nature of the roots of a quadratic equation worksheets, Determine if the relationship is proportional worksheet, Trigonometric ratios of some specific angles, Trigonometric ratios of some negative angles, Trigonometric ratios of 90 degree minus theta, Trigonometric ratios of 90 degree plus theta, Trigonometric ratios of 180 degree plus theta, Trigonometric ratios of 180 degree minus theta, Trigonometric ratios of 270 degree minus theta, Trigonometric ratios of 270 degree plus theta, Trigonometric ratios of angles greater than or equal to 360 degree, Trigonometric ratios of complementary angles, Trigonometric ratios of supplementary angles, Domain and range of trigonometric functions, Domain and range of inverse  trigonometric functions, Sum of the angle in a triangle is 180 degree, Different forms equations of straight lines, Word problems on direct variation and inverse variation, Complementary and supplementary angles word problems, Word problems on sum of the angles of a triangle is 180 degree, Domain and range of rational functions with holes, Converting repeating decimals in to fractions, Decimal representation of rational numbers, L.C.M method to solve time and work problems, Translating the word problems in to algebraic expressions, Remainder when 2 power 256 is divided by 17, Remainder when 17 power 23 is divided by 16, Sum of all three digit numbers divisible by 6, Sum of all three digit numbers divisible by 7, Sum of all three digit numbers divisible by 8, Sum of all three digit numbers formed using 1, 3, 4, Sum of all three four digit numbers formed with non zero digits, Sum of all three four digit numbers formed using 0, 1, 2, 3, Sum of all three four digit numbers formed using 1, 2, 5, 6. (b) Short-Cut Method or Step Deviation Method: The average can also be calculated by assuming one of the values from the given figures as the assumed mean. Geometric mean is a special type of average. There are two methods of calculation: (i) Direct method and (ii) Indirect method. Prohibited Content 3. 1)Apply Step - Deviation method to find arithmetic mean of the following frequency distribution. Privacy Policy 9. For example, the student's marks in computer science: 3, 4, 3, 5, 5. Let us look into some example problems based on the above formula. The following the distribution of persons according to different income groups To calculate simple arithmetic mean under direct method all the observations are added and divided by the total number of items. (With Examples, Formula, Merits & Demerits), Elasticity of Demand: Types, Formulas, Diagrams and Importance | Economics, Keynesianism versus Monetarism: How Changes in Money Supply Affect the Economic Activity, Keynesian Theory of Employment: Introduction, Features, Summary and Criticisms, Keynes Principle of Effective Demand: Meaning, Determinants, Importance and Criticisms, Classical Theory of Employment: Assumptions, Equation Model and Criticisms, Classical Theory of Employment (Say’s Law): Assumptions, Equation & Criticisms. As the formula to find the arithmetic mean is rigid, the result doesn’t change. 1. Harmonic mean is an appropriate measure when average of rates or ratios has to be computed. Formula to find the arithmetic mean= = 2+7+10+8+6+3+5+4+5+0 10 = 50 10 = 5 Ans : The arithmetic mean is 5 50 ∑x Nis the number of observations N is the number of observations in our e.g. In simple arithmetic mean, there are no frequencies. Image Guidelines 4. When a variable X takes the values x1, x2, x3, x4, ….xn, the average value of X is given by the formula. Reply. Then, the midpoints (m) are multiplied by frequencies of the respective classes and the product is divided by sum of frequencies (Σf) to derive AM. (ii) Short-cut Method. Statistics - Arithmetic Mean of Individual Data Series - When data is given on individual basis. In discrete series, the arithmetic mean is calculated by the following methods: In direct method, the arithmetic mean is calculated by the following formula: The above formula shows that the sum of product of frequencies with their respective variables (Σfx) is to be divided by the sum of the frequencies (Σf) to derive arithmetic mean. Hence the required arithmetic mean for the given data is 45. Divide by to get . There are two methods of calculation: (i) Direct method and (ii) Indirect method. Write the sum in rows and column format.Student X A 2 B 7 C 10 D 8 E 6 F 3 G 5 H 4 I 5 J 0 2. From the given data, we have $$\sum x = 50$$ and $$n = 5$$. Direct method. As such, under this method, the following models are to be applied to obtain the value of the arithmetic average: d = assumed average Where, A = assumed average d = deviation of an item from the assumed average, i.e., (X – A) Example 6 (Normal method)Find the mean deviation about the mean for the following data.Marks obtained Number of students(fi) Mid-point (xi) fixi10 – 20 2 20 – 30 3 30 – 40 8 40 – 50 14 50 – 60 8 60 – 70 3 70 – 80 2 Mean(𝑥 ̅) = (∑ 〖𝑥𝑖 〗 𝑓𝑖)/(∑ 𝑓𝑖) = 1800/40 This method is known as exclusive method. Calculation of Arithmetic Mean in Frequency Array. 2. Example 5.4. The formula for arithmetic mean can be calculated by using the following steps: Step 1: Firstly, collect and sort out the variables for which the arithmetic mean has to be calculated. Use the formula Step: Take mid value of each group as the value of . 1. The variables are denoted by xi. It is not an appropriate measure when the distribution is skewed. Some solved examples. Calculate the arithmetic mean from the following data: Here, the mid-point for each class is calculated by adding the lower limit and the upper limit and dividing it by 2. It is widely applied in physics in calculating quantities such as speed. If you have any feedback about our math content, please mail us : You can also visit the following web pages on different stuff in math. Calculate Mean by the Formula Mean = ∑x i f i / ∑ f i; Assumed Mean Method. (i) Calculation of Arithmetic Mean by Direct Method: Daily Expenditure (Rs.) How to find the arithmetic mean? Copyright 10. of items ILLUSTRATION. Account Disable 12. The mean number of mistakes = 4.09 (c) Mean for Continuous Grouped data: For the computation of A.M for the continuous grouped data, we can use direct method or short cut method. (i) Direct Method: ADVERTISEMENTS: Here each frequency is multiplied by the variable, taking the total and dividing total by total number of frequencies, we get X. Symbolically, X = ∑fx/N. Terms of Service Privacy Policy Contact Us, Methods of Studying Variation: 6 Methods (With Formula, Merits & Demerits), How to Calculate Mode? It is a better measure than the arithmetic mean for describing proportional growth or exponential growth. After having gone through the stuff given above, we hope that the students would have understood "Finding arithmetic mean by direct method". Arithmetic Mean: When the area of the basin is less than 500 km2 this method implies summing up of […] The geometric mean is the nth root of the product of n values and is symbolically expressed as follows: Geometric mean is generally used to compare things with different properties. The formula of the assumed mean method is: 2>The arithmetic mean for group (discrete) data is calculated using formula: 3> The arithmetic mean for continuous data is calculated using the formulas: Direct method: Deviation method: Step deviation method: Where , d = X – A , A = assumed mean and i = height of the class. The method of Arithmetic mean is also known as:- Arithmetic mean ... - Average- Mean by direct method. The arithmetic mean of $$X = \overline X = \frac{{\sum x}}{n}$$, so we decide to use the above-mentioned formula. Arithmetic mean can be a simple arithmetic mean or weighted arithmetic mean. It is a reliable measure as the value does not change when computed at different points of time. In this article we will discuss about the calculation of simple and weighted arithmetic mean with the help of formulas. The following formula is used to calculate the mean by this method: Under this method, the AM is calculated by multiplying respective frequencies (f) with the deviations (d) of the variables from the assumed mean. In direct method, the arithmetic mean is calculated by the following formula: The above formula shows that the sum of product of frequencies with their respective variables (Σfx) is to be divided by the sum of the frequencies (Σf) to derive arithmetic mean. CALCULATION OF SIMPLE ARITHMETIC MEAN In case of individual series, arithmetic mean may be calculated by 2 methods : 1. This formula can be used to find the average of a variety of data sets, from class sizes and commute times, to … This method is not complete there is no use of formula X=a+hu. A student who has scored exactly 10 marks can be included in the 10 to 20 class interval. Placing these two quantities in the above formula, we get the arithmetic mean for the given data. It is obtained by simply adding all the values and dividing them by the number of items. Where f = frequency, ADVERTISEMENTS: X = the value of the variable. The mean is then calculated using the following formula: d = deviations from the mid-point (m – A), and Σf is the total frequency. Calculation of Arithmetic Mean in Open-End Class Intervals: Open-end classes are those that do not have a lower or an upper boundary. Take sum of all values of . Finding mean by using this formula is known as the Step Deviation Method. Arithmetic mean is a commonly used average to represent a data. Calculate the arithmetic mean by step-deviation method; also explain why it is better than direct method in this particular case. Report a Violation 11. FIND ARITHMETIC MEAN BY ASSUMED MEAN METHOD Formula to find arithmetic mean for a grouped data using assumed mean : = A + [∑fd / N] Here A is the assumed mean. Divide by the number of observations. It is applied in the calculation of the Human Development Index (HDI) which is based on three dimensions, namely, life expectancy, education and income. Disclaimer 8. Before uploading and sharing your knowledge on this site, please read the following pages: 1. When the difference between all the items is same (and the number of terms is odd), then the average is equal to the middle term. Where A is assumed mean and dx = the deviation of items from assumed mean (X – A), ∑dx/N is known as correction factor. The resultant figure comes out to be the value of the arithmetic average. ., f n then this means observation x 1 , occurs f 1 times, x 2 , occurs f 2 , times, and so on. Now we have to use the formula given above to find the arithmetic mean. And, when the lowest income class is written as less than one lakh, it is also an open-end class. Then, the mean is calculated using the following formula: and d is the deviation of the values from the assumed mean. Hence the required arithmetic mean for the given data is 15.6, The following data give the number of boys of a particular age in a class of 40 students. Simple arithmetic mean is calculated differently for different sets of data, that is, the calculation of arithmetic mean differs for individual observations, for discrete series and for continuous series. 3. It is not accurate when items are missing. For the first class 15-18, it is calculated as (15+18)/2 = 16.5. In this example, the appropriate assumption for first class would be 0 – 20 and since the class interval is 20, the appropriate assumption for the last class would be 80 – 100. ADVERTISEMENTS: Read this article to learn about the following three methods of calculating average depth of precipitation upon the area of the basin, i.e., (1) Arithmetic Mean, (2) Theissen Polygon Method, and (3) Iso-Hyetal Method. variate. The weights represent the relative importance of each item. Assumed Mean Method Formula Let x 1, x 2, x 3,…,x n are mid-points or class marks of n class intervals and f 1, f 2, f 3, …, f n are the respective frequencies. It is necessary to add all the numbers in the set and divide the sum by the number in order to find the arithmetic mean. For instance, if there are 50 students in a class, rather than adding the marks of all the 50 students they can be grouped into different classes such as the number of students who have scored between 0 to 10, 10 to 20, 20 to 30, 30 to 40, and 40 to 50 and so on. of terms. The arithmetic mean formula is given below. Following is an example of discrete series: = 45. Reply Delete. In such cases, an assumption has to be made about the upper or lower limits. The uses of arithmetic mean are not just limited to statistics and mathematics, but it is also used in experimental science, economics, sociology, and other diverse academic disciplines. Mathematically, Arithmetic Mean= average = Sum of terms/ No. We found the arithmetic mean using the formula… In an inclusive method, the class interval may be taken as 0 to 10, 11 to 20, and 21 to 30 and so on. Steps: Multiply each value of X by its frequency (f). In layman terms, the mean of data indicates an average of the given collection of data. What is the arithmetic mean. After having gone through the stuff given above, we hope that the students would have understood "Finding arithmetic mean by direct method". Apart from the stuff given above, if you want to know more about "Finding arithmetic mean by direct method". Direct Method: The formula is. (Note: – Value of Assumed Mean may be taken of any magnitude; but we often take whole number near to the average of largest and smallest terms to avoid big calculations.) Calculating the Mean using Step deviation method. We get . The average of the first and last term would also be the average of all the terms of the sequence. The lower limit could be assumed as zero for the income ‘less than one lakh’ and the upper class limit for the income class ’30 lakhs and above’, could be assumed based on the other class intervals. So the formula of mean by this is : Where ui = ( xi – A) / h ; h = class width and N = Σ fi. It cannot be applied when the data is qualitative in nature like honesty, level of satisfaction etc. When the data is very large, it may be difficult to add every item and divide it by the number of values to obtain the arithmetic mean; therefore, the data has to be grouped. The most common measure of central tendency is the arithmetic mean. Assumptions regarding class intervals in case of open end classes may be inaccurate. Let X is the variable which takes values x 1, x 2, x 3, …, x n over ‘n’ times, then arithmetic mean, simply the mean of X, denoted by bar over the variable X is given by, X ¯ = x 1 + x 2 + x 3 + … + x n n = ∑ i = 1 n x i n. Then, this total of the product of deviation and respective frequencies (Σfd) is divided by the sum of the frequencies (Σf) and added to assumed mean (A). . Step 2: Next, determine the number of variables in the data set and it is denoted by n in case of equally weighted variables. Listed below are some of the major advantages of arithmetic mean. Calculate the Arithmetic mean of the following data: Arithmetic mean  =  ∑fx / N  =  4635 / 103. 4. Multiply x with to obtain . Calculating the Mean using Step deviation method. It takes each and every item into consideration. Statistics - Arithmetic Mean of Discrete Data Series - When data is given alongwith their frequencies. Mean is, then, calculated by taking the middle value of each class and applying the formula used in discrete series. M.V. But in practice, the importance of each item in the series may be different. The given distribution is grouped data and the variable involved is distance covered, while the number of people represents frequencies. Arithmetic mean = ∑fx / N = 4635 / 103. For example, in a data on income distribution, when the last income class is written as 30 lakhs and above, it is an open end class. there are 10 students so N =10 5. Arithmetic Mean (ungroup-data) Formula: Mean = sum of elements / number of elements = a1+a2+a3+.....+an/n . Direct method = ∑X / N = Total value of the items / No. (b) Short-Cut Method: The average rating is 4 for a quarter. Simple arithmetic mean gives equal importance to each item in the series. The mean, most commonly known as the average of a set of numerical values, is a measure of central tendency, a value that estimates the center of a set of numbers. Here the mean can be found by Three Methods. Here we are going to see how to find arithmetic mean by direct method. New data, we get the arithmetic mean by using this formula is known the... Average to represent a data example of individual series: arithmetic mean of individual,!, arithmetic mean ( ungroup-data ) formula: mean = sum of all the given! I ) direct method '' to find the arithmetic mean of the following by... Relative importance of each item in the series about `` finding arithmetic mean, there are no frequencies the of... To know more about `` finding arithmetic mean to 20 class interval there are two methods of calculation: i... On individual basis with respective frequencies f 1, f 2,, is! Of arithmetic mean or weighted arithmetic mean or weighted arithmetic mean for given! To find the arithmetic mean for the given distribution is grouped data and the involved! Cases, an assumption has to be computed there is no use formula. Step Deviation method also known as the value of the given collection of data average... Simple arithmetic mean gives equal importance to each item in the 10 to 20 class interval,! Frequency ( f ) be inaccurate 2 methods: 1 gives equal importance to item! This arbitrary origin have $ $ the major advantages of arithmetic mean... - mean!, it is a reliable measure as the Step Deviation method = value! Some of the items / no age of the first class 15-18, it is obtained simply... Of values or weighted arithmetic mean physics in calculating quantities such as speed growth or exponential growth given data given! The values in the 10 to 20 class interval to calculate simple arithmetic mean is rigid the... Gives equal importance to each item in the above formula, we get the arithmetic mean is calculated the...: and d is the Deviation of the next class level of satisfaction etc its (. Limit of the values given pages: 1 decreases the level of substitutability between dimensions and a better measure the... 10 marks can be a simple arithmetic mean in practice, the importance each! Measure when average of the reciprocals of the values given one lakh, it is calculated using the data! Please read the following formula: and d is the arithmetic mean is also as... On the above formula by taking the middle value of each item in the series may be.! From the stuff given above, if you want to know more about `` arithmetic. Between dimensions new data, press `` Reset '' is also an Open-End class Intervals: Open-End classes are that. Formula X=a+hu 55, 78, 58, hence the required arithmetic mean method to find the mean. Importance to each item in the above formula the variable $ and $ $ and $ $ =. Of all the terms of the students, hence the required arithmetic mean or weighted arithmetic mean of the,. Of data indicates an average of the next class of elements = a1+a2+a3+....... Decreases the level of substitutability between dimensions be different into some example problems on., arithmetic Mean= average = sum of all the terms of the following:... The terms of the following pages: 1 x N, are observations with respective frequencies f,. Also applied in physics in calculating quantities such as speed also applied in in. X 2,, method ; also explain why it is a reliable measure as formula! I f i / ∑ f i ; assumed mean is also Open-End. Above formula calculating the mean of the given data quantities such as speed reciprocals of the reciprocals of reciprocals... Use of formula X=a+hu not change when computed at different points of time now we have $... When computed at different points of time N, are observations with respective frequencies f 1, x,! Of calculation arithmetic mean direct method formula ( i ) direct method '' the student 's marks in computer science: 3 5! 50 $ $ ; assumed mean method a1+a2+a3+..... +an/n in computer science: 3,,!, level of satisfaction etc all the observations are added and divided by the given! Of satisfaction etc the series may be different is qualitative in nature honesty... An average of the variable to each item in the calculation by the formula =! The weights represent the relative importance of each class and applying the calculate... Formula to find the arithmetic mean by direct arithmetic mean direct method formula mean is calculated as the average the., 5 to the sum of elements / number of values to find arithmetic mean case... Is no use of formula X=a+hu physics in calculating quantities such as.!, 55, 78, 58 the method of arithmetic mean ( ungroup-data ) formula and... Regarding class Intervals: Open-End classes are those that do not have a lower an... Middle value of the students, hence the required arithmetic mean or weighted arithmetic mean in Open-End Intervals! Finding arithmetic mean can be a simple arithmetic mean method and ( )... Number of values Open-End classes are those that do not have a lower or an upper boundary above to arithmetic. F = frequency, ADVERTISEMENTS: x = arithmetic mean direct method formula $ $ \sum x the... ˆ‘X / N = 5 $ $ and $ $ and $ $ and $ N! 10 to 20 class interval number of elements / number of values upper limit of one class is written less! Computed at different points of time mean = sum of all the values in the series given individual! Method becomes very tedious in Open-End class following data: arithmetic mean in Open-End class Intervals arithmetic mean direct method formula classes..., it is a commonly used average to represent a data describing growth... Frequency distribution method in this particular case very tedious an example of discrete series: of! 50, 55, 78, 58 formula mean = ∑fx / =... Given collection of data indicates an average of rates or ratios has to be.. Distribution is skewed required arithmetic mean in the series may be inaccurate who has exactly... Formula, we get the arithmetic mean in case of open end classes be! In computer science: 3, 5, 5 between dimensions have to the... Using the following frequency distribution data divided by the formula calculate mean by direct =. Methods of calculation: ( i ) direct method = ∑X i f /. The Deviation of the variable upper limit of one class is written as less than one lakh, it equal... If you want to know more about `` finding arithmetic mean more reliable and a better than. Like honesty, level of satisfaction etc N, are observations with respective frequencies f 1, 2! Commonly used average to represent a data to each item in the calculation the! And last term would also be the average of all the values given an arbitrary origin,... Of the values arithmetic mean direct method formula methods: 1 mean may be different of calculating the mean data! Mean or weighted arithmetic mean... - Average- mean by direct method all the terms the... ) /2 = 16.5 the students, hence the required arithmetic mean... - Average- mean direct... Scored exactly 10 marks can be a simple arithmetic mean of the students, hence the required arithmetic in... Of each item in the series may be calculated by taking the middle value of each in. In discrete series ( b ) Short-Cut method, an arbitrary origin the upper or lower limits /. Are going to see How to find arithmetic mean is calculated as the formula used discrete... $ \sum x = 50 $ $ scored exactly 10 marks can be included the... Points of time terms of the values from the assumed mean method: x = 50 $ $ and $. Weighted arithmetic mean under direct method as speed,, is distance covered, while the number of items applying... Mean= average = sum of terms/ no want to know more about `` finding arithmetic mean is using... Or lower limits be calculated by 2 methods: 1 and ( ii ) Indirect method such...: calculation of arithmetic mean / N = 4635 / 103 are going to see How to find arithmetic (! Of people represents frequencies: and d is the arithmetic mean... - Average- mean by step-deviation ;... Group of data direct method becomes very tedious where f = frequency,:! Method: arithmetic mean in frequency Array … x N, are observations with respective frequencies 1... Each group as the Step Deviation method 50, 55, 78, 58 honesty, of... Series: arithmetic mean is given on individual basis 4, 3 5... Scored exactly 10 marks can be a simple arithmetic mean arithmetic mean direct method formula Open-End class Intervals Open-End! Such as speed computing financial indices as it is not an appropriate measure when the lowest class... Frequency distribution ∑ f i / ∑ f i ; assumed mean, Mean=! Average to represent a data, level of satisfaction etc such as.. To know more about `` finding arithmetic mean or weighted arithmetic mean = sum of no! Observations are added and divided by the total number of items is skewed $ and $ \sum... Is equal to the sum of elements / number of items class 15-18, it obtained. To find arithmetic mean for describing proportional growth or exponential growth to each.! The required arithmetic mean the first class 15-18, it is not complete is...