Two pipes can fill a tank in 15 minutes and 15 minutes. An outlet pipe can empty the tank in 45 minutes. If all the pipes are opened when the tank is empty, then how many minutes will it take to fill the tank? Choose the correct choice from the following options
A) 1 / 15	B) 1 / 16	C) 1 / 11	D) 1 / 9	E) 1 / 12

Rationale: "part of the filled by all the three pipes in one minute = 1 / 15 + 1 / 15 - 1 / 45 = 1 / 9 so , the tank becomes full in 9 minutes . answer : d"
Answer: D