The average of 12 numbers is 47. The average of the first 5 numbers is 45 and the average of the next 4 numbers is 52. If the 10th number is 10 less than the 11th number and is 5 more than the 12th number, then what is the average value of the 11th and 12th numbers?
Show answer & explanation
Correct answer: A
Explanation
The correct answer is Option 4 i.e. 44.5.
Sum of 12 numbers = 12 × 47 = 564
Sum of first 5 numbers = 45 × 5 = 225
Sum of next 4 numbers = 4 × 52 = 208
Sum of first 9 numbers = 225 + 208 = 433
Now, X = XI - 10 and X = XII + 5
So, 433 + X + X + 10 + X - 5 = 564
⇒ 3X = 564 - 438
⇒ x = 42
Now, XI = 52 and XII = 37
Required average = (52 + 37)/2 = 44.5