Two pipes A and B can fill a cistern in 10 and 15 minutes respectively. Both fill pipes are opened together,but at the end of 3 minutes, ‘B’ is turned off. How much time will the cistern take to fill ?
Choose the correct choice:
A) 6 min B) 8 min C) 10 min D) 12 min E) None of these
In one min, (A + B) fill the cistern = 1⁄10 + 1⁄15 = 1⁄6th   In 3 min, (A + B) fill the cistern = 3⁄6 = 1⁄2th   Remaining part = 1 - 1⁄2 = 1⁄2   ∵ 1⁄10th part filled by A in one min.   ∴ 1⁄2nd part filled by A in 10 × 1⁄2 = 5 min.   ∴ Total time = 3 + 5= 
<gadget id="calculator">3 + 5</gadget>
<output>8</output>
8 min.   Answer 8 min
<result>B</result>
Two pipes A and B can fill a cistern in 10 and 15 minutes respectively. Both fill pipes are opened together,but at the end of 3 minutes, ‘B’ is turned off. How much time will the cistern take to fill ?