A father tells his son, "I was 3 times of your present age when you were born." If the father's present age is 48 years, how old was the boy 4 years ago?

Suppose that son's age before 4 years = P
Present age of the son = P + 4
At son's birth father's age = 3(P + 4) = 3P + 12
The father's present age = (3P +12) + (P + 4) = 48
⇒ 4P = 48 years – 16 = 32
⇒ P = 8 years
Therefore, 4 years ago the boy was = 12 – 4 = 8 years