Question

four large pipes will drain a pond in 6 hours and 12 small pipes will drain the same pond in 4 hours.How long will it take 2large pipes and 2small pipes to drain the pond?

Answer 1

if nine large pipes can drain a pond in eight hours, and six small pipes can drain the same pond in sixteen hours, how long will it take three large pipes and five small pipes to drain the pond? give your answer in hours and minutes. 
Answer by Alan3354(60957)   (Show Source): You can put this solution on YOUR website!
if nine large pipes can drain a pond in eight hours, and six small pipes can drain the same pond in sixteen hours, how long will it take three large pipes and five small pipes to drain the pond?
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I assume all "large pipes" are the same size, and same for small pipes.
9 large pipes take 8 hours --> 1/8 of the pond drained per hour for 9
--> 1/72 pond per hour per large pipe.
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6 small pipes take 16 hrs --> 1/16 pond/hr for 6
--> 1/96 pond/hr per small pipe.
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3 large can do 3/72 ponds/hr = 1/24
5 small can do 5/96 ponds/hr
1/24 + 5/96 = 9/96 ponds/hr total = 3/32 ponds/hr
--> 32/3 hours per pond
= 10 hours 40 minutes