Riddle: There is a boat that only holds 180 pounds. There are a set of twins that weighs 90 pounds each. And their uncle weighs exactly 180 pounds. They all need to get to the other side of the river. None of them have taken swimming lessons, they don't know how to swim and have no swimming devices to help them. How do they get to the other side of the river without going over maximum weight?
Answer: Both twins get in the boat and they will weigh 180 pounds together. one twin drops off the other. The twin remaining goes back. The uncle gets in and goes alone. That will be 180 pounds by himself. He goes to the other side and gets out. The twin gets in and gets the other and goes back to the other side and meets the uncle.