A bus and a truck are driving on two parallel highways. Bus length150m, truck length 250m. If two cars are driving in opposite directions, it takes 10 second from the moment when the front of the two cars meet to the moment when the rear of the car leaves. If a bus chases a truck from behind, it takes 100 second to catch up with the back of the truck from the front of the bus to leave the front of the truck. Find the speed of two cars.

Solution: (1) The sum of the speeds of two cars is: (250+150) ÷10 = 40m/s; (2) The speed of bus is faster than that of truck: (250+150) ÷100 = 4m/s; (3) The truck speed is: (40-4) ÷ 2 =18m/s; (4) Bus speed:18+4 = 22m/s.