SOLUTION: one pump can drain a pool in 9 minutes. When a second pump is also used, the pool only takes 5 minutes to drain. How long would it take the second pump to drain the pool if only on

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Question 570697: one pump can drain a pool in 9 minutes. When a second pump is also used, the pool only takes 5 minutes to drain. How long would it take the second pump to drain the pool if only one pump is used?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let the time to drain the pool for 2nd pump = t
The 1st pump's rate of draining is +1%2F9+
which means ( 1 pool ) / ( 9 min )
The 2nd pump's rate of draining is +1%2Ft+
which means ( 1 pool ) / ( t minutes )
Together, their rate of draining is +1%2F5+
------------------------------
To find the rate when both are used, add their
individual rates
+1%2F9+%2B+1%2Ft+=+1%2F5+
Multiply both sides by +45t+
+5t+%2B+45+=+9t+
+4t+=+45+
+t+=+11.25+
+.25%2A60+=+15+
The 2nd pump can drain the pool in 11 min and 15 sec
operating alone