One pipe can fill a tank three times as fast as another pipe. If together the two pipes can fill the tank in 39 minutes, then the slower pipe alone will be able to fill the tank in
Choose the correct choice
A) 144 mins  B) 140 mins  C) 136 mins  D) 156 minw  E) None of these
Explanation:   Let the slower pipe alone fill the tank in x minutes   then faster will fill in x/3 minutes.   Part filled by slower pipe in 1 minute = 1/x   Part filled by faster pipe in 1 minute = 3/x   Part filled by both in 1 minute =   1/x+3/x=1/39   =&gt;4/x=1/39   x=39∗4=156 mins   Option 156 minw
<result>D</result>
One pipe can fill a tank three times as fast as another pipe. If together the two pipes can fill the tank in 39 minutes, then the slower pipe alone will be able to fill the tank in