Gustav’s father is seven times as old as he is. A year ago, he was nine times as old as Gustav. Find Gustav’s present age.

Answer 1

The Present:
Son: X yrs old.
Father: 7X yrs old.

A year ago:
Son: (x-1) yrs old.
Father: 9(X-1) yrs old.

The difference between their ages is the
same as last year:
7x-x = 9(x-1)-(x-1)
6x = 9x-9-x+1
-2x = -8
X = 4 yrs = The son's age.