Question

A is 15 years older than B. Ten years ago,A was four times of B's age. What's are their ages now?

Answer 1

Suppose A's age now is x years.
Since A is 15 years older than B, B's age now is x - 15 years.
10 years ago, A's age was x - 10 years.
10 years ago, B's age was (x-15)-10 = x-25 years.
Since 10 years ago, A's age was 4 times B's age, we have
x-10 = 4(x-25)
x-10 = 4x - 100
4x - x = -10+100
3x = 90
x= 30 years
so A's age now = 30 years
and B's age now = x-15 = 15 years.
Answer: A: 30 years; B: 15 years