A father tells his son, "l was three 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? 

Present age of the son=- 12 years The father was 36 years old when the boy was born. = 12 x 3 = 36 years 0 + 12 = 12 years and 36 + 12 = 48 years Therefore, 4 years ago the boy was = 12 - 4 = 8 years