SOLUTION: If a water tank takes 5 minutes to fill and 7 minutes to empty.If the drain is left open when being filled, how long dose it take to fill the tank.

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Question 599515: If a water tank takes 5 minutes to fill and 7 minutes to empty.If the drain is left open when being filled, how long dose it take to fill the tank.
Answer by w_parminder(53) About Me  (Show Source):
You can put this solution on YOUR website!
Rate of filling the tank = 1/5
Rate of emptying the tank = 1/7
as these two works are exactly opposite in nature, so while filling the tank with its drain open, the combination formula becomes
1%2FC=1%2F5-1%2F7
1%2FC=%287-5%29%2F35
1%2FC=2%2F35
C = 35/2 = 17.5
So the tank would be filled in 17 min & 30 sec