SOLUTION: A father can wash a car in 20 min and his son can wash a car in 5 min. If they togather start to wash a car how much time will be required?

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Question 889110: A father can wash a car in 20 min and his son can wash a car in 5 min. If they togather start to wash a car how much time will be required?
Answer by Edwin McCravy(20056)   (Show Source): You can put this solution on YOUR website!
A father can wash a car in 20 min and his son can wash a car in 5 min. If they togather start to wash a car how much time will be required?
What??  The father takes 4 times as long as his son?  I don't believe anybody
can wash a car, and do a good job, in 5 minutes.  This problem is either
botched or very unrealistic.  However I'll do it anyway:


The father's washing rate in cars per minute is 1 car per 20 minutes or



The son's very speedy washing rate in cars per minute is 1 car per 5 minutes
or

.

Suppose the answer is x minutes.

Then their combined washing rate in cars per minute is 1 car per x minutes or

  

The equation comes from 

    

    

Multiply through by LCD = 20x and solve.  The answer is 
x = 4 minutes.

Edwin
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