Two pipes can fill a tank in 10 minutes and 25 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 answers: A) 30 minutes B) 17 minutes C) 7 minutes D) 10 minutes E) 12 minutes
Part of the filled by all the three pipes in one minute   = 1/10 + 1/25 - 1/45 = (45 + 18 - 10)/450 = 53/450   So, the tank becomes full in 7 minutes.   Answer: 7 minutes
<result>C</result>
Two pipes can fill a tank in 10 minutes and 25 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?