SOLUTION: water from tank is being used for irrigation at the same time that the tank is being filled.the inlet pipe can fill the tank in 80 hours .the two outlet pipes can drain it in 8 and

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Question 755342: water from tank is being used for irrigation at the same time that the tank is being filled.the inlet pipe can fill the tank in 80 hours .the two outlet pipes can drain it in 8 and 4 hours .how long will it take the pipes to drain the tank if all three pipes are operating at the same time .
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Add the rate of filling and subtract
the rates of draining
Let +t+ = the time in hrs to drain the tank
+-1%2F8+-+1%2F4+%2B+1%2F80+=+-1%2Ft++
Note that the right side says that the result is a
rate of draining, not filling
Multiply both sides by +80t+
+-10t+-+20t+%2B+t+=+-80+
+-29t+=+-80+
+t+=+80%2F29+
+t+=+2.76+ hrs
+.76%2A60+=+45.6+
It will take 2 hrs and 45.6 min to drain the tank