If one person washed a car in 6 minutes and another person washes the same car in 8 minutes. how long will it take to wash the car together?

In 8 minutes they can wash 2 and ⅓ cars (Al finishes his car and gets (8-6)/6 or ⅓ of the way into a third car). Round off 2 and ⅓ to 2.333 cars in 8 minutes. Therefore the time to wash one car working together is  1.166 in 4 minutes. So less than four minutes.

So, assume the work is 6*8 = 48 units, 

then Person #1 works @ 8 units/min 
Person #2 works @ 6 units/min 
together they work @ 14 units/min 

time needed = 48/14 = 24/7 
= 3 3/7 min 

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