Question

A pipe can fill a tank in 20 minutes and another pipe can fill it in 30 minutes. A person opens both the pipes simultaneously. When the tank should have been full, he finds that the drain pipe is open. He then closes the drain pipe and after three minutes, the tank is full. In how much time can the drain pipe empty the tank?

Answer 1

Answer:

waste pipe has emptied the 4/6=2/3 part of bath in 6 mins.

Rest 1/3 part of tank can be emptied by the waste pipe in 6/2=3 mins.