An electric pump can fill a tank in 2 hours. Because of a leak in the tank, it was taking 21⁄2 hours to fill the tank. The leak can drain all the water off the tank in how many hours?
A man travelled a distance of 61 km. in 9 hours , partly by walking at speed of 4 km / hr and partly on bicycle at speed of 9 km / hr. The distance covered by walking is