The average of a group of men is increased by 5 years when a person aged of 18 years is replaced by a new person of aged 38 years. How many men are there in the group?

Explanation:-

Let N be the no. of persons in the group.
Required number of person is given by;
Member in group* aged increased = difference of replacement
N*5 = 38-18
Or, 5N = 20
Or, N = 4.