the mean of 9 numbers

First of all, we better find out the sum of the 9 numbers

Sum of the 9 numbers = 9 X 12 = 108

Then, Sum of the first 5 numbers = 5 X 8 = 40

Therefore, sum of the other four numbers = 108 - 40 = 68

And so, the mean of the other four numbers

= 68 / 4

= 17

The answer is D.

The answer is really detailed!