A pump can fill a tank with water in 1 hour. Because of a leak, it took \(1{1\over3}\) hours to fill the tank. In how many hours can the leak alone drain all the water of the tank when it is full?
Five men and 2 boys can do as much work in 30 days as 7 men and 10 boys can do in 15 days. How many boys should join 40 men to do the same work in 4 days?