SOLUTION: Pipe A can fill a tank in 15hrs. Pipe A & B can fill it in 6hrs. How long for pipe B by itself to fill the tank?

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Question 995963: Pipe A can fill a tank in 15hrs. Pipe A & B can fill it in 6hrs. How long for pipe B by itself to fill the tank?
Found 2 solutions by josmiceli, fractalier:
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Add their rates of filling to get rate filling together
A's rate:
[ 1 tank filled ] / [ 15 hrs ]
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Let +t+ = time in hrs for pipe B to fill tank alone
B's rate:
[ 1 tank filled ] / [ t hrs ]
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Their rate working to gether:
[ 1 tank filled ] / [ 6 hrs ]
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+1%2F15+%2B+1%2Ft+=+1%2F6+
Multiply both sides by +30t+
+2t+%2B+30+=+5t+
+3t+=+30+
+t+=+10+
B alone can fill the tank in 10 hrs
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check:
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+1%2F15+%2B+1%2Ft+=+1%2F6+
+1%2F15+%2B+1%2F10+=+1%2F6+
+2%2F30+%2B+3%2F30+=+5%2F30+
+5%2F30+=+5%2F30+
OK

Answer by fractalier(6550) About Me  (Show Source):
You can put this solution on YOUR website!
The setup is
t/A + t/B = 1
Plugging in we get
6/15 + 6/B = 1 (where 1 represents one job or one tank)
6/B = 1 - 2/5 = 3/5
and
B = 10 hours