Question

A father is now three times as old as his son. Five years back, he was four times as old as his son. The age of the son is :
1) 12
2) 15
3) 18
4) 20

Answer 1

Let x denotes father's age and y denotes son's age.
by the given question, x=3y and x-5=4(y-5)
or, 3y-5=4y-20
or, 3y-4y=-20+5
or,-y=-15
or, y=15
Then x=3y=3.15=45
Then father's age is 45 years and son's age is 15 years.