One pipe can fill a tank three times as fast as another pipe. If together the two pipes can fill the tank in 86 minutes, then the slower pipe alone will be able to fill the tank in	Choose the correct choice
A) 81 min	B) 108 min	C) 144 min	D) 192 min	E) None
Solution   Let the slower pipe alone fill the tank in x minutes.   Then, faster pipes will fill it in x/3 minutes.   Therefore, 1/x + 3/x	= 1/36   ‹=› 4/x = 1/36   ‹=› x= 144 min.   Answer 144 min
<result>C</result>
One pipe can fill a tank three times as fast as another pipe. If together the two pipes can fill the tank in 86 minutes, then the slower pipe alone will be able to fill the tank in