Chance can wash the car in 2 hours, while Sandy can wash the same car in 4 hours. How many hours would it take for them to wash the car together?

Question

imstuck · Answer

This is a work problem.  If Chance can wash a car in 2 hours, he can get 1/2 the job done in 1 hour.  If Sandy can wash the car in 4 hours, she can get 1/4 of the job done in 1 hour.  So your equation looks like this:

imstuck · Answer

$$\frac{ 1 }{ 2 }+\frac{ 1 }{ 4 }=\frac{ 1 }{ x }$$That 1/x is the amount of time it will take them to get the whole job done.

imstuck · Answer

Find the least common multiple to rid yourself of the denominators and solve for x.  4x is the LCM.  Like this:

imstuck · Answer

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