Four years ago, the average of son’s and father’s age was 27.5. Today, the ratio of their age is 5:16. Find out the son’s present age.

Suppose the present age of Sun is 5x and father’s age is 16x as mentioned in question 5:16.
Age of Son 4 Years ago=5X-4
Age of Father 4 Years ago=16x-4
The Average of their ages before 4 years ago=27.5
[(5x-4) – (16x-4)] / 2=27.5
(21x-8) / 2=27.5
21x -8=27.5*2
21x-8=55
21x=55+8
21x=63
x-63/21
x=3
The age of Son was 5x as mentioned in question
5x=5 * 3=15 Years