Question

If the mean of x1,x 2 is 7.5 and the mean of x1 ,x2 ,x3 ,is 8 then the value of x3 is

Answer 1

Mean = sum of variables/number of variables.

First equation

X1 + X2 = 7.5

______

2

X1 + X2 = 15 ------ (1)

Second equation

X1 + X2 + X3 = 8

__________

3

X1 + X2 + X3 = 24 -------- (2)

Subtract equation 1 from equation 2

(X1 + X2 + X3) - (X1 + X2) = 24 - 15

X3 = 9

Answer 2

Find the sum of x1 and x2:

Mean of x1 and x2 = 7.5 (Given)

Sum of x1 and x2 = 7.5 x 2 = 15

Find the sum of x1, x2 and x3:

Mean of x1, x2 and x3 = 8 (Given)

Sum of x1,  x2 and x3  = 8 x 3 = 24

Find x3:

x3 = Sum of x1,  x2 and x3 - Sum of x1 and x2

x3 = 24 - 15

x3 = 9

Answer: The value of x3 is 9