Question 58150: In a nearby animal park there is a large aquarium that holds many types of rare and exotic fish. The maintenance department has the responsibility of periodically removing the fish, draining the water, and giving the tank a thorough cleaning. Once it has been cleaned, it is filled again and the fish are returned for the public to view and enjoy.
This week it is Wilbur's turn in the job assignment rotation to do the work. He opens the drain to remove the water, noting that his watch says 9:55A.M. As the last drop runs out, he looks at his watch again; it says 10:11A.M.
Now Wilbur sets to work cleaning and scrubbing the inside of the tank, not even noticing that he is working right through his lunch break. As he finishes the work, he realizes that he is quite hungry. In his haste to go eat, he quickly turns on the two pipes that are always used to fill the tank, but forgets to put the plug in the drain spout. He leaves at 12:40P.M.
Here you need to know to facts. One pipe can fill the whole tank by itself in 20 minutes, while the other requires 30 minutes to do the same task.
When Wilbur finishes his lunch, he returns to see how full the tank is now. It is nearly full, so he decides to wait until the water reaches its proper height in the tank. At the moment it does, he turns off the two pipes and notes the time on his watch.
What is that time?
Answer by stanbon(75887)   (Show Source):
You can put this solution on YOUR website! He leaves at 12:40P.M.
Here you need to know to facts. One pipe can fill the whole tank by itself in 20 minutes, while the other requires 30 minutes to do the same task.
When Wilbur finishes his lunch, he returns to see how full the tank is now. It is nearly full, so he decides to wait until the water reaches its proper height in the tank. At the moment it does, he turns off the two pipes and notes the time on his watch.
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1st Pipe DATA:
Time to fill tank = 20 min/job ; rate = 1/20 job/min
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2nd Pipe DATA:
Time to fill tank = 30 min/job ; rate = 1/30 job/min
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Pipes together DATA:
Time to fill tank = x min/job ; rate = 1/x job/min
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EQUATION:
1st pipe rate + 2nd pipe rate = together rate
1/20 +1/30 = 1/x
50/600 = 1/x
600/50=x
x=12 minutes (The two pipes together will take 12 min to fill tank)
He should shut them off at 12:40 + 12 min = 12:52 PM
Cheers,
Stan H.
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