Percy is 8 years older than Ginny. In ten years time he will be three times Ginny’s present age. How old is Percy now?
Let P = Percy's present age
Let G = Ginny's present age
P = G + 8 (Percy is 8 years older than Ginny)
P + 10 = 3*G (In ten years time he will be three times Ginny’s present age)
Substituting for P = G + 8 into the 2nd eqn,
G + 8 + 10 = 3G
18 = 2G
G = 9
P = 17