The average of N numbers is 21. If a number 57 is removed, then average becomes 17. What is the value of N?
1). 10
2). 8
3). 9
4). 11
Average of N numbers = 21
The sum of N numbers = 21N
Now,
⇒ 21N - 57 = 17(N - 1)
⇒ 21N - 17N = 57 - 17
⇒ 4N = 40
⇒ N = 10
Hence, the value of N = 10