One pipe can fill a tank four times as fast as another pipe. If together the two pipes can fill the tank in 36 minutes, then the slower pipe alone will be able to fill the tank in:  Choose the correct choice from the following answers:
A) 180 min B) 160 min C) 280 min D) 18 min E) 190 min
Let the slower pipe alone can fill the tank in x minutes   Then the faster pipe can fill the tank in x/4 minutes   Part filled by the slower pipe in 1 minute = 1/x   Part filled by the faster pipe in 1 minute = 4/x   Part filled by both the pipes in 1 minute = (1/x)+(4/x)   180 minnswer is 180 min   It is given that both the pipes together can fill the tank in 36 minutes   ⇒ Part filled by both the pipes in 1 minute = 1/36   (1/x)+(4/x)=1/36   5/x=1/36   x=5×36=180   i.e.,the slower pipe alone fill the tank in 180 minutes
<result>A</result>
One pipe can fill a tank four times as fast as another pipe. If together the two pipes can fill the tank in 36 minutes, then the slower pipe alone will be able to fill the tank in: