Bunuel wrote:

A hotel began draining its swimming pool at a constant rate at 7am. Beginning at 12pm, the rate tripled because of evaporation. If the pool began completely full and was 3/4 full at 9:30am, at what time was the pool completely empty?

A. 12:45pm

B. 1:20pm

C. 1:40pm

D. 2:10pm

E. 2:15pm

The hotel began draining the swimming pool(which was completely full) at 7 AM.

At 9:30 AM(2 hours 30 minutes later), the pool was 3/4th full (or) 1/4th of the pool was drained.

At 12:00 PM(2 hours 30 minutes later), working at the same rate, another 1/4th of the pool was drained.

Now, the pool was half full at 12 AM.

It has been given that the draining rate triples because of evaporation after 12 PM.

Initially, 5 hours(300 minutes) was needed to drain the pool to half its capacity,

at 3 times the rate, we would be needing \(\frac{300}{3} = 100\) minutes to drain the pool now.

Therefore, the pool was completely empty at

1:40 PM(Option C) - 100 minutes after 12 PM

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