The average of 10 numbers is 15. The average of 8 of these numbers is also 15. What is the average of the remaining two numbers?

Question: The average of 10 numbers is 15. The average of 8 of these numbers is also 15. What is the average of the remaining two numbers?

Solution:
Average of 10 numbers = 15
∴ Total sum of 10 numbers = 10 × 15 = 150

And,
Average of 8 numbers = 15
∴ Sum of 8 numbers = 8 × 15 = 120

∴ Sum of remaining 2 numbers = 150 - 120 = 30

∴ Average of remaining 2 numbers = 30/2 = 15