Two pipes A and B can separately fill a cistern in 80 minutes and 160 minutes respectively. There is a third pipe in the bottom of the cistern to empty it. If all the three pipes are simultaneously opened, then the cistern is full in 40 minutes. In how much time, the third pipe alone can empty the cistern?	Pick one:
A) 90 min B) 160 min C) 110 min D) 120 min E) 130 min
1/40-(1/80+1/160)=-1/160   third pipe can empty in 160 minutes   ANSWER:160 min
<result>B</result>
Two pipes A and B can separately fill a cistern in 80 minutes and 160 minutes respectively. There is a third pipe in the bottom of the cistern to empty it. If all the three pipes are simultaneously opened, then the cistern is full in 40 minutes. In how much time, the third pipe alone can empty the cistern?