Question

A family is on a road trip. The speed limit during the first 125 miles of the trip is 55 mph, and the speed limit during the last 180 miles is 75 mph. How many miles per hour over the speed limits must they drive in order to arrive at their destination in 4.5 hours? ____ mph over.

Answer 1

The speed limit during the first 125 miles of the trip is 55 mph.

`t=(d)/(s)=(125)/(55)=2.3\: \text{hours}`

So, it will take 2.3 hours to cover the first 125 miles.

Since the total time to arrive at the destination is 4.5 hours, then it means that they have to cover the rest of the distance in 4.5 - 2.3 = 2.2 hours

`s=(d)/(t)=(180)/(2.2)=81.8\: \text{mph}`

So, the speed for the remaining distance must be 81.8 mph which is 81.8 - 75 = 6.8 mph over the limit.

Therefore, 6.8 mph over the limit.