The average of 25 numbers is 18. The average of the first 12 of these numbers is 14 and that of the last 12 of these numbers is 17. The 13th number is:
Answer & explanation
Correct answer: option 2
Sum of 25 numbers = 25 x 18 = 450
Sum of first 12 numbers = 12 x 14 = 168
Sum of last 12 numbers = 12 x 17 = 204
13th number = 450 - 168 - 204 = 78