It's a complicated algebra problem. She does pretty good considering that she doesn't have pencil, paper, and a calculator.
The big brother is 4 years old. His little brother is half his age. When the big brother is 100 years old, how old will the little brother be?
-via Tastefully Offensive
The real question is: after driving her around the bend with that riddle, how old will he be when he gets laid again?
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