Water flow

[vittalgmat]

Water flows into an empty tank of 54 liters via 12 small pipes. The rate of each pipe is 1 liter per hour. However, water flows out of the tank via several big pipes at the rate of 1.5 liter per hour. If after 12 hours, the tank is completely full, how many big pipes are there?

A. 2.5
B. 3
C. 4
D. 5
E. 6

[spoiler]OA: D[/spoiler]
I am looking for multiple ways to solve this problem.
Pls help.

thanks in advance.

[logitech]

IN - OUT = NET

12 x 1 lt/hr x 12 hr - 12 hr x 1.5 lt/hr x N = 54

144 - 18N = 54

N = 5

Oh by the way answer choice A is funny 2.5 pipes

[vittalgmat]

IN - OUT = NET

12 x 1 lt/hr x 12 hr - 12 hr x 1.5 lt/hr x N = 54

144 - 18N = 54

N = 5

Oh by the way answer choice A is funny 2.5 pipes

Thanks Logitech.

2.5 .. dint realize until u pointed it out .. A broken pipe I suppose. Or a pipe with a semi circular cross-section.!!

[vivek.kapoor83]

Solved it in 30 sec

let y be the big pipes

then 54/(12-y*1.5) = 12
solving for Y = 5

or by backsolving also it should not take more than 45 sec i think