Andrew and Stephen drive on the highway in the same direction at respective rates of 72 and 80 kmh. If Stephen is 4 km behind Andrew, by how much does he have to increase his speed to catch up with Andrew in 20 minutes?
Can someone explain this in detail?
In 20 minuets, Andrew can drive 20 (72/60) = 24 km
Since Andrew is already 4 km ahead of Stephen, Stephen has to cover 28 km in 20 minuets.
Then, the km/h speed for Stephen would be = (28/20)60 = 84.
Increased speed = 84 - 80 = 4km/h