Question

When Janice is 20 years old; her brother is half her age. When Janice is 30 years old; how old is her brother?

Answer 1

20 years old
Her brother

Answer 2

When Janice was 20, her brother was 10.

Since the age between them will always be 10 years,

30-10= 20

When Janice is 30, her brother is 20.

I hope this helps!
~cupcake