In 10 years A will be twice as old as B was 10 years ago. If A is now 9 years older than B, what is the present age of B?

Let the present age of B and A be x and ( x + 9 ) years; then, Age of B and A after 10 years will be x + 10 and x + 9 + 10; According to question, In 10 years A will be twice as old as B was 10 years ago 2(x - 10) = x + 9 + 10 2x - 20 = x + 19 ⇒ 2x - x = 19 + 20 ∴ x = 39 years