To protect his country a king decided to build a wall made out of stone along the border. The wall had to be 3 meters thick and 5 meters high. The border of the country has a length of 500 kilometers. Assuming that one cubic meter of stone weights about 3000 kg, how much heavier becomes the earth by building this wall?

Sue has six pairs of white gloves and six pairs of pink gloves in her drawer. In complete darkness, how many gloves should she at least take from the drawer in order to be sure to get a pair that match?

Mom, Dad, and two kids have come to a river, and they find a boat. It is small and can only carry one adult or two kids at a time. Both kids are good rowers, but how can the whole family reach the other side of the river?