Question

The average of 18 numbers is 30. The average of 1st 8 numbers is 17 and the average of the last 8 numbers is 25. What is the average of the 9th and 10th numbers?

• A. 204
• B. 102
• C. 67
• D. 52

Answer 1

Answer:

B. 102

The sum of 18 numbers is (18 × 30) = 540 The sum of 1st 8 numbers is ( 17 × 8) = 136 The Sum of the last 8 numbers is ( 25 × 8) = 200 9th number + 10th number = Sum of 18 numbers - (sum of 1st 8 numbers + Sum of last 8 numbers) = 540 - ( 136 + 200) = 540 - 336 = 204 The average of the 9th and the 10th number = 204 / 2 = 102