THE CORRECT ANSWER IS (E). YOU CAN ANSWER THIS QUESTION WITHOUT RE...
18. The correct answer is (E). You can answer this question without resorting to formal
algebra. The drainpipe empties the pool at half the rate that the inlet pipe fills the pool.
So it makes sense that if both pipes are fully open, after 3 hours the pool will only be
half full. (The inlet pipe fills the pool, but at the same time the drainpipe empties half
the pool.) It follows that it takes 6 hours to fill the pool to capacity with both pipes fully
open. You can also solve this problem algebraically. Letting x equal the number of hours,
subtract the drainpipe’s rate from the inlet pipe’s rate (subtract because the drainpipe
works against the inlet pipe), using the “work” formula:
x
3
2
x
6
5
1
Multiply both sides by 6, then solve for x:
2x
2
x
5
6
x
5
6