If the mean of 5 observations x, x + 2, x + 4, x + 6, and x + 8 is 11, then the mean of the last three observations is -

Question: If the mean of 5 observations x, x + 2, x + 4, x + 6, and x + 8 is 11, then the mean of the last three observations is -

Solution:
ATQ,
{x + (x + 2) + (x + 4) + (x + 6) + (x + 8)}/5 = 11
⇒ 5x + 20 = 55
⇒ 5x = 55 - 20
⇒ x = 35/5
∴ x = 7

So, the numbers are 7, 9, 11, 13, 15

Required mean = (11 + 13 + 15)/3
= 39/3
= 13