Question 146930: please help!!!!!!!!!!!!
jim can fill a pool carrying bucks of water in 30min. sue can do the same job in 45min. tony can do the same in 1 1/2 hours. how quickly can all three fill the pool together?
A.12min
B.15min
C.23min
D.28min
E.21min
Answer by Alan3354(69443)   (Show Source):
You can put this solution on YOUR website! jim can fill a pool carrying bucks of water in 30min. sue can do the same job in 45min. tony can do the same in 1 1/2 hours. how quickly can all three fill the pool together?
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The trick with this type of problem is to find "the trick." Obviously, you can't add the times because it should take less time with more people working (at least mathematically, when people get together they might talk a lot and not work at all).
The trick is to use the inverses. Jim can fill 1 pool in 30 minutes. Instead of looking at the minutes per pool, use pools per minute, the inverse.
Jim - 1 pool/30 mins
Sue - 1 pool/45 mins
Tony- 1 pool/90 mins
Add these up.
1/30 + 1/45 + 1/90 = (3 + 2 + 1)/90 = 1/15
Working together, they can do one pool per 15 minutes.
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