Question

Harry is 10 years old, and his brother Bill is twice as old. When Harry is 20 how old will bill be?

Answer 1

If Harry's brother Bill is twice as old as him when Harry is 10, that makes bill 20. In another 10 years (when harry is 20) bill will be 30.

Answer 2

INFORMATION:

Harry is 10
Bill is twice as old as Ben

QUESTION:
How old will bill be when harry is 20

EQUATION
Let bill be x, so....

2(10) + 10 = x
20 + 10 = x
30 = x

So Bill will be 30