Question

Q. Two pipes A and B can fill a tank in
12 and 16 minutes respectively. Both
pipes are opened together, but 4
min before the tank is full, pipe A is
closed. In how many minutes will
the tank be full?
(A) 9 min 8 sec
(B) 10 min 9 sec
(C) 11 min 19 sec
(D) 11 min 29 sec
(1) C (2) A (3) B (4) D​

Answer 1

Answer:

(2) A 9min 18sec

Step-by-step explanation:

both can fill in one minute = 1/12 + 1/16 = 7/48 part

means both can fill in 48/7min

now A stopped before 4min

hence time spent for filling is

= 48/7 - 4 = 20/7 min

the part filled in this (20/7) time

= 7/48 × 20/7 = 5/12

remaining part =1 - 5/12 = 7/12

but B takes 16min for full (1)

so B takes for 7/12 part = 7/12 × 16 = 9.3333min

the remaining time to fill = 9min 18 sec

Note

0.3 min = 0.3 × 6 = 0.18sec