Since, both the pipes are opening one by one. So, in 2 minutes, part of Tank will be filled =
1
6
+
1
8
=
7
24
So, in 6 minutes 3 × 7/24 = 21/24 part will be filled. Remaining part = 1 – 21/24 = 1/8 part Now it’s A’s turn to fill the tank. SO time taken to fill 1/8 part =