Question: If the average of 5 numbers is 15, what is the average of the first three numbers if the last two numbers are 10 and 20?

Options:

1. 10
2. 15
3. 20
4. 25

Correct Answer: 20

Solution:

Total of 5 numbers = 5 * 15 = 75. Total of last two numbers = 10 + 20 = 30. Total of first three numbers = 75 - 30 = 45. Average of first three = 45 / 3 = 15.