a family decided to spend the weekend in phoenix they drove

a family decided to spend the weekend in phoenix. they drove out on friday, they hit no traffic and made the trip in 4 hours. when they came home sunday however, they encountered a lot of traffic.their average speed on the return trip was 15mph slower then the speed on thier friday drive to phoenix,and it took them 5 hours to get home.how far is phoenix from their home?

Solution

Assume when they drove to Phoenix with speed x miles/hr.
then the speed ofthe returned trip is x-15 miles/hr.
We have 4 x = 5(x-15), so x = 75.
And the required distance is 75*4 = 300 miles