Question

Three years ago, Marry was three times as old as his brother. Five years from now he will be twice as old as his brother. How is Marry now?

Answer 1

3 years ago:
m - 3 = 3(b - 3)
m - 3 = 3b - 9
m + 6 = 3b
m/3 + 2 = b

5 years from now:
m + 5 = 2(b + 5)
m + 5 = 2b + 10
m - 5 = 2b
m/2 - 5/2 = b

combine:
m/3 + 2 = m/2 - 5/2

1. multiply by 6
2m + 12 = 3m - 15

2. add 15 - 2m to both sides
27 = m

Marry is 27 years old.