Question 741238
It takes 48 hours to fill a swimming pool with water using 3 identical water pumps. 
A) how long would it take to fill the pool if there were 8 of these pumps?
Filling the pool takes 48*3 = 144 pump-hours
144 pump-hrs/8 pumps = 18 hours
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B) how many pumps would be needed to fill the pool in 12 hours?
144 pump-hrs/12 hrs = 12 pumps
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Notice how the units cancel.  Including the units can help avoid errors.