A girl is 21 years old and her brother is a third her age. When the girl is 36, what will be the age of her brother?
21 divided by 3 = 7
That means the brother is 14 years younger.
36 - 14 = 22
The brother will be 22 years old.
a third of 21=21/3=7
in how many years
36-21=15
in 15 years
7+15=22
age is 22