Answer:
It will take 4 hours and 48 minutes with both pipes.
Step-by-step explanation:
Add their rates of filling
1st pipe's rate = ( 1 tank ) / ( 12 hrs )
2nd pipe's rate = ( 1 tank ) / ( 8 hrs )
Let, t = hrs to fill tank using both pipes
(1 / 12) + (1 / 8) = (1 / t)
Multiply both sides by 24t
2t + 3t = 24
5t = 24
t = 4.8
0.8 x 60 = 48
It will take 4 hours and 48 minutes with both pipes