Question

A certain list consists of 21 different numbers. if n is in the list and n is 4 times the average (arithmetic mean) of the other 20 numbers in the list, then n is what fraction of the sum of the 21 numbers in the list?

Answer 1

If x is the average of "the other 20 numbers", then their sum is 20x. Adding the 21st number makes the sum of all 21 numbers be 20x +4x = 24x.

The 21st number, 4x, is 4x/(24x) = 1/6 of the total of all numbers,