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If the numerical values of xi and fi are large and computation of product of xi and fi
becomes tedious and time consuming, assumed mean method is used. In this method

a)one among xi, is chosen as the assumed mean denoted by ‘A’

b)the difference di between a and each of the xi’s .i.e. di = xi – A is calculated.

c) Calculate the sum of frequencies as and the total sum of the values as  fidi

d) Mean =

Exa:-3-Find the mean of the following data.

Marks 10 - 14 15 - 19 20 - 24 25 - 29 30 - 34
Number of 4 6 12 5 3
students

Solution:

Marks Number of students Mid value f id i
f i x i

10-14 4 12 -10 -40
15-19 6 17 -5 -30
20-24 12 22 0 0
25-29 5 27 5 25

30-34 3 32 10 30
Total

A = 22, ,

Mean =

Therefore, mean = 21.5

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