Two cars start at the same time, but travel in opposite directions. one car's average speed is 20 miles per hour (mph). at the end of 4 hours, the two cars are 320 miles apart. find the average speed in mph of the other car. (enter an exact number.)
Let s= the speed of the other car.
Think of this as one of the cars standing still and the other moving at the sum of their speeds.
350=(20+s)*4
350=80+4s
4s=350-80
4s=270
s=270/4
s=67.5
The average speed of the other car is 67.5 mi/hr.
