Al can wash a car in 60 minutes, and bill can wash a car in 30 minutes. cathy can wash a car in 20 minutes. how long, in minutes, would it take the 3 of them to wash a car, working together?
To figure this out you need to average the numbers. To average them you add them all up and divide by how many are there. (60+30+20)/3 (90+20)/3 110/3 36
