Name: Lisa

Who is asking: Student
Level: All

Question:
Al washes a car in six hours. Fred washes a car in eight hours. How long will it take them to wash a car together?

Hi Lisa,
Eight hours to wash a car! Is it a railroad car?

The way to look at this problem is to consider the rate at which each of them washes a car. Al washes at one eighth of a car per hour and Fred at one sixth of a car per hour. Thus together they wash at (1/6 + 1/8) = 7/24 of a car per hour. Hence to wash one car they would have to work 24/7 or 3 4/7 hours.

Cheers,
Harley