Question

0
Two pipes. A & B can fill a tank in 12 & 16 minutes respectively. Both pipes are opened together, but 4 minutes before
the tank is full, pipe A is closed. In how many minutes will the tank be full?
A. 9 minutes 8 seconds
10 minutes 9 seconds
C 11 minutes 19 seconds
D. 11 minutes 29 seconds
HE​

Answer 1

Answer:

Lets, both pipe are open together x min.

A can fill in 1 min is 1/12 part of the tank.

B can fill in 1 min is 1/16 part of the tank.

so, both can fill in 1 min=(1/12)+(1/16) =7/48 part of the tank

both can fill in x min=7x/48

only B can fill in 4 min after closed A.

Now,

(7x/48)+(4/16)=1

(7x+12)/48=1

7x=48-12

x=36/7=5 min 8 sec (approx)

so the tank fill in =4 min+5 min 8sec

=9 min 8 sec