Beginning at noon yesterday, water was removed from a partially filled

Beginning at noon yesterday, water was removed from a partially filled water tank at a constant rate of 300 liters per hour. When there were 600 liters of water left in the tank, no more water was removed from the tank. Were there more than 1,000 liters of water in the tank at noon yesterday?

Observe that the question essentially asks whether more than 400 liters of water was removed or whether the water removal lasted more than 400/300 = 4/3 hours (80 minutes).

(1) There were 600 liters of water in the tank at 2:00 yesterday afternoon.

It's unclear when the removal stopped. It could have been any time between noon and 2:00 pm. If it stopped right at 2:00 PM, then the water was removed for two hours, totaling 2*300 = 600 liters. In this case, the initial amount in the tank would be 600 + 600 = 1,200 liters. However, if the removal stopped earlier, say at 1:00 pm, only 300 liters would have been removed, making the initial amount 600 + 300 = 900 liters. Hence, this statement alone is not sufficient.

(2) There were more than 650 liters of water in the tank at 1:00 yesterday afternoon.

Since 300 liters were removed between noon and 1:00 pm, the initial amount was more than 650 + 300 = 950 liters. But this doesn't specify how much more than 950 liters, so it's unclear if it exceeded 1,000 liters. This statement alone is also not sufficient.

(1)+(2) We still don't know the exact time when the water removal stopped. Therefore, we still cannot definitively say if there were more than 1,000 liters in the tank at noon. For example, consider the following two cases:

• Case 1: If the water removal lasted for 2 hours (until 2:00 pm), then the initial amount in the tank was 1,200 liters (at 1:00 pm - 900 liters, which is more than 650 liters).
  
• Case 2: If the water removal lasted for 4/3 hours (80 minutes) (until 1:20 pm), then the initial amount in the tank was 600 + 4/3*300 = 1,000 liters (at 1:00 pm - 700 liters, which is more than 650 liters)

Not sufficient.

Answer: E.
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Similar question to practice (also from GMAT Prep Focus): https://gmatclub.com/forum/beginning-at ... 23224.html
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Bunuel, how did you deduce this part? Observe that the question essentially asks whether more than 400 liters of water was removed or whether the water removal lasted more than 400/300 = 4/3 hours (80 minutes).

when it is 600 liters, the removal stops.

For water to be >1000 liters at the beginning,
Removal has to be >1000-600 or >400 liters
Time spent in removing has to be greater than \(\frac{1000-600}{300}\) or >\(\frac{4}{3}\)
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Beginning at noon yesterday, water was removed from a partially filled water tank at a constant rate of 300 liters per hour. When there were 600 liters of water left in the tank, no more water was removed from the tank. Were there more than 1,000 liters of water in the tank at noon yesterday?

(1) There were 600 liters of water in the tank at 2:00 yesterday afternoon.
We have TWO hours ( 1200 to 1400h) to remove water.
It could have started with a max of 600+2*300 or 1200 liters and the minimum could be 600 liters itself.
So, possible range is 600 to 1200 liters. => \(600\leq W\leq 1200\)
Insuff

(2) There were more than 650 liters of water in the tank at 1:00 yesterday afternoon.
So, We have ONE hour ( 1200 to 1300h) to remove water.
It could have started with a max of anything and the minimum could be 650+300 liters itself.
So, \(950\leq W\leq Infinity\)
Insuff

Combined
the common range is \(950\leq W\leq 1200\)
Insuff
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Hello Bunuel, in your explanation above how can you assume that it may have stopped pumping out water after 1pm? The question says: water was removed from a partially filled water tank at a constant rate of 300 liters per hour. Once it hit 600 liters it stopped. This makes me assume that it was continuously pumping out water at the rate of 300 liters per hour. So if in 2 hours it pumped out 600 and had 600 remaining, capacity was 1200 imo.­

­The statement "There were 600 liters of water in the tank at 2:00 yesterday afternoon" doesn't guarantee that pumping stopped precisely at 2:00 PM. It's possible pumping ceased earlier, maintaining the 600-liter level afterward. 
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Bunuel

I re-read the question and this is what I focus on:

water was removed from a partially filled water tank at a constant rate of 300 liters per hour. When there were 600 liters of water left in the tank, no more water was removed from the tank.

I assumed it is a continuous operation till the target is met. Why would it stop earlier?

Posted from my mobile device

­You're missing a key point. Just because there were 600 liters of water in the tank at 2:00 yesterday afternoon doesn't necessarily mean that the pumping stopped precisely at 2:00. It simply indicates that it reached 600 liters no later than 2:00. It could have hit 600 liters before 2:00 and then remained at that level afterward: 2:00, 3:00, and so on.
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