Question 18
A pump is filling a tank with water at a constant rate while water in the tank is also drained by 3 identical pipes. Starting from a full tank with water being pumped into it, the tank can be completely drained by the 3 identical pipes in 35 minutes. If an additional identical pipe is installed, a full tank can be completely drained in 20 minutes while water is pumped into it. How many minutes will it take for the pump to fill an empty tank to its brim without any draining pipe?