The average of 11 numbers is 68. The average of the first four numbers is 78 and that of the next four numbers is 63. The 9th is two times the 11th number and the 10th number is less than the 11th number what is the average of 9th and 11th numbers?
Show answer & explanation
Correct answer: C
Explanation
The correct answer is Option 3 i.e. 70.5
| Application |
|
Average of 11th number = 68 Sum of 11th Number = 11 × 68 = 748. Average of 1st 4 numbers = 78 Sum of 1st 4 numbers = 78 × 4 = 312. Average of next 4 numbers = 63 Sum of next 4 numbers = 63 × 4 = 252. Let 11th number = x So, 9th number = 2x 10th number is less than 11th number = 748 - (312 + 252) = 184 Then 9th + 10th + 11th = 184 2x + (x - 4) + x = 184 x = 47. Hence the average of 9th amd 11th number = (47 + 94)/2 = 70.5 |