A 12 gallon tub has a faucet that lets water in at a rate of 3 gallons per minute, and has a drain that lets water out at a rate of 5 gallons per minute. If you start with 3 gallons of water in the tub, how long will it take to fill the tub completely?

A    6 minutes

B    7minutes

C    8 minutes

D    9 minutes

Solution

Correct Answer: Option A

 

12 gallon tub,with 3 gallons of water in the tub: needs {{{9Gal}}} to fill water in at 3 gal/min, and out at a rate of 1.5 gal/min: Net in at {{{1.5gal/min}}}  {{{9gal/1.5 (gal/min)}}} = 6 min

 

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