Question

The average of 21 numbers is 66. The average of the first 9 numbers is 63.7 and that of the last 13 numbers is 69.9. If the 9^th number is excluded, then what is the average of the remaining numbers?
1. 63
2. 64
3. 64.5
4. 63.5

Answer 1

Correct Answer - Option 3 : 64.5

Given:

The average of 21 number is 66

Calculation:

⇒ Total sum of 21 number = 21 × 66 = 1386

⇒ The sum of first 9 number = 63.7 × 9 = 573.3

⇒ The sum of last 13 number = 69.9 × 13 = 908.7

⇒ The 9th number = 1386 - 573.3 - 908.7 = 96

⇒ When 9th number is excluded than sum = 1386 - 96 = 1290

⇒ New average = 1290/20 = 64.5

∴ The required result will be 64.5.