Numerical answer
Pipes A and B can fill an empty tank in 20 minutes and 30 minutes respectively, while pipe C can empty the full tank in 15 minutes. All three pipes are opened together on the empty tank, and after 10 minutes pipe C is closed. How many more minutes will it take to fill the tank?
Show answer and solution
Answer: 10
Take tank capacity = 60 units (LCM of 20, 30, 15). A fills 3 units/min, B fills 2, C empties 4.
All three together: 3 + 2 − 4 = 1 unit/min, so in 10 minutes 10 units are filled.
Remaining 50 units at A + B's rate of 5 units/min ⇒ 10 more minutes.
All three together: 3 + 2 − 4 = 1 unit/min, so in 10 minutes 10 units are filled.
Remaining 50 units at A + B's rate of 5 units/min ⇒ 10 more minutes.
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