Question

Percy is 8 years older than Ginny. In ten years time he will be three times Ginnys present age. How old is Percy now?

Answer 1

Now,
G - Ginny's age.
P=G+8, Percy's age.

In 10 years,
G + 10 - Ginny's age in 10 years.
P+10 -  Percy's age in 10 years.

 In ten years time Percy (P+10) will be three times Ginnys present age (3G).
P+10=3G

Now we have 2 equations, and we can write a system of equations.

(1)     P=G+8
(2)     P+10=3G  -------> G=(P+10)/3, we need to substitute it into equation 1.

( P=(P+10)/3+8)   /*3
3P=P +10+24
2P = 34
P = 17

Percy is 17 years old now.

Check,
P=17, G=17-8=9
P+10=3G , 17+10=3*9, 27 = 27 True