SSC CPO 2019 PYQ — Question 136

Understanding

Application

The average of ten number is 72.

So,

Sum of 10 numbers = 720

The average of the first four number is 69 and that of the next three numbers is 74.

So,

Sum of first 7 numbers

= 69 × 4 + 74 × 3

= 498

So,

Sum of 8^th, 9^th and 10^th numbers = 720 – 498 = 222

The 8^th number is 6 more than the 9^th number and 12 more than the 10^th number.

Suppose 10^th number = x

So,

8^th number = (x + 12)

9^th number = (x + 12 – 6) = (x + 6)

So,

x + (x + 12) + (x + 6) = 222

⇒ 3x = 204

⇒ x = 68

So,

8^th number = 68 + 12 = 80

And

9^th number = 68 + 6 = 74

Hence,

Required average

= [80 + 74]/2

= 77