George drove a distance of d kilometers at 60 km/h. He averaged 45 km/h on the return trip. In terms of d, how much time did he spend driving?

Answer 1

The total time is (t₁ +t₂)

according to definition of average speed V_avg= distance / time elapsed, and then t=distance/ V_avg

That gives t₁=d/v1=d/60 and t₂=d/45

Thus, t_tot= d (1/60 +1/45) =25d/12

Answer 2

As George drove a distance of d kilometers at 60 km/h on the first trip, he spent d/60 hours driving on this portion of the trip. On the return trip, he averaged 45 km/h, so he spent d/45 hours driving as he has to drive a distance of d kilometers back. This means that he spent d/60 + d/45 hours driving, which when simplified gives us d/60 + d/45 = 3d/180 + 4d/180 = 7d/180 hours driving.