Question

If mean of five observations x+1, X+2, X+3.
and x+5 is 15, then mean of first three observa
tions is
RRB NTPC 2016
(a) 12
(b) 13
(d) 15
(e) 14​

Answer 1

Given,

$\frac{(x + 1) + (x + 2) + (x + 3) + (x + 4) + (x + 5)}{5} = 15 \\ = > \frac{5x + 15}{5} = 15 \\ = > 5x + 15 = 75 \\ = > x = 12$

Then, the first three numbers are 13, 14 and 15.

Thus there mean = 42/3 = 14

Hence, the answer is d) 14

HOPE THIS COULD HELP!!!