Mark is 6 years old. His sister Tina is half of his age. So when Mark is 100 years old, how old is Tina?
Answer
Tina will be 97 years old when Mark is 100 years old.
When Tom was 6 years old, Tina was 3 years old. 94 years later, he becomes 100 years old. And 94 years later, his sister will be 97 (94 + 3) years old.