Hello.
Let's call the initial speed 'x'. When driving at that speed, Jeremy's father takes 20 minutes to arrive to the school. When driving 18 mph faster (x + 18), he gets there in 12 minutes. Therefore:
20 - x
12 - x + 18
As they're inversely proportional:
12 - x
20 - x + 18
That means that the initial speed is of 27mph. Since we have the time and the speed, we can find the distance:
Average Speed = Total Distance Travelled / Time Interval
20 minutes = 0.33h
Hope I helped and good luck.
Let's call the initial speed 'x'. When driving at that speed, Jeremy's father takes 20 minutes to arrive to the school. When driving 18 mph faster (x + 18), he gets there in 12 minutes. Therefore:
20 - x
12 - x + 18
As they're inversely proportional:
12 - x
20 - x + 18
That means that the initial speed is of 27mph. Since we have the time and the speed, we can find the distance:
Average Speed = Total Distance Travelled / Time Interval
20 minutes = 0.33h
Hope I helped and good luck.