A cistern can be filled by two pipes filling separately in 12 and 16 minutes separately. Both the pipes are opened together for a certain time but being clogged, only `7/8` of the full quantity of water flows through the former and only `5/6` through the latter pipe. The obstructions, however, being suddenly removed, the cistern is filled in 3 minutes from that moment. How long was it before the full flow began? `2 1/2m in` b. `\ 3 1/2m in` c. `4 1/2m in` d. `1/2m in`

Options

A. 8 min
B. 3 min
C. 5.6 min
D. 4.5 min

Answer

D