Question

The mean of five observations x + 1, x + 4,2+5, x + 7 and x + 8 is 15. Find the value of
hence find the mean of the first three observations.​

Answer 1

$\sf \Large Solution!!$

Mean = 15

Number of observations = 5

Sum of observations = x + 1 + x + 4 + 2 + 5 + x + 7 + x + 8

Sum of observations = 4x + 27

Mean = Sum of observations ÷ Number of observations

15 = (4x + 27) ÷ 5

15 × 5 = 4x + 27

75 = 4x + 27

75 - 27 = 4x

4x = 48

x = 48 ÷ 4

x = 12

Finding the mean of first three observations.

Sum of observations = (x + 1) + (x + 4) + (2 + 5)

Sum of observations = (12 + 1) + (12 + 4) + (7)

Sum of observations = 13 + 16 + 7

Sum of observations = 36

Number of observations = 3

Mean = Sum of observations ÷ Number of observations

Mean = 36 ÷ 3

Mean = 12

Mean of first three observations = 12