William travels to school in two different ways. Either he walks to school and takes the bus home, or he takes the bus to school and walks home. In each case his total travelling time is 40 minutes. If he were to take the bus both ways, his total travelling time would be 20 minutes. How many minutes would it take if he walked both ways?
Since it takes the bus 20 minutes to travel from his home to school and from school to home, that means it takes the bus: 20 / 2 = 10 minutes to travel from home to school or vice versa.
But, when he walks from home to school and takes the bus from school to home, it takes him 40 minutes. That means his walking from home to school, or vice versa, takes him: 40 - 10 = 30 minutes.
Therefore, if he walked both ways, it would take him:
30 x 2 = 60 minutes, or one hour.