Two pipes can fill a tank in 20 and 12 hours, while third pipe will make the tank empty in 20 hours. If all three pipes operate simultaneously. In how many hours the tank will be filled ? Pick one:
A) 5 Hours B) 7 Hours C) 8 Hours D) 9 Hours E) 12 Hours
In 1 hour it fill 1/20 + 1/12 - 1/20 = 1/12   So fill tank fill up in 12 Hours   ANSW12 HoursR:12 Hours
<result>E</result>
Two pipes can fill a tank in 20 and 12 hours, while third pipe will make the tank empty in 20 hours. If all three pipes operate simultaneously. In how many hours the tank will be filled ?