One fill pipe A is 3 times faster than second fill pipe B and takes 10 minutes less time to fill a cistern than B takes. Find when the cistern will be full if fill pipe B is only opened.
Choose the most appropriate option:
A) 20 min
B) 18 min
C) 15 min
D) 10 min
E) None of these
Let B can fill the cistern in x min. Then,   then A can fill the cistern in x⁄3 min   Given x - x⁄3 = 10 ⇒ x = 15 min   Answer 15 min
<result>C</result>
One fill pipe A is 3 times faster than second fill pipe B and takes 10 minutes less time to fill a cistern than B takes. Find when the cistern will be full if fill pipe B is only opened.