One pipe can fill a tank four times as fast as another pipe. If together the two pipes can fill the tank in 40 minutes, then the slower pipe alone will be able to fill the tank in? Choose the correct choice from the following:
A) 100min
B) 150min
C) 200min
D) 250min
E) 300min
Let the slower pipe alone fill the tank in x minutes   Then, faster pipe will fill it in x/4 minutes   1/x + 4/x = 1/40   5/x = 1/40   x = 200 min   Answer is 200min
<result>C</result>
One pipe can fill a tank four times as fast as another pipe. If together the two pipes can fill the tank in 40 minutes, then the slower pipe alone will be able to fill the tank in?