A man with 90 sheep wants to sell them in a market 30km away from his farm. He went searching for trucks to load his sheep and he found out that every truck can carry 30 sheep at a time, but he will have to pay 1 sheep for every 1km to every truck driver (1sheep/km/driver).
At the end of the day he managed to sell 25 sheep, how is that possible?
(If you do a simple math you realize that he’ll arrive at the market with no sheep
1 sheep x 30 km x 3 drivers = 90 sheeps) (excuse my english)