Question

A plane can fly 640 miles in the same time as it takes a car to go 240 miles. If the car travels 100 mph slower than the plane, find the speed (in mph) of the plane.

Answer 1

Let s be the speed of the plane. Then s - 100 is the speed of the car.

640/s = 240/(s - 100)

640(s - 100) = 240s

8(s - 100) = 3s

8s - 800 = 3s

5s = 800, so s = 160 mph

The speed of the plane is 160 mph, and the speed of the car is 60 mph.