Answer: Choice B
A pool is filled with water using one valve. A little time after the pool is filled to its capacity, the pool needs to be emptied because of some problems. Then the pool is refilled immediately, using two valves this time.
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Explanation:
The parts where the graph goes uphill, as you move from left to right, is when the pool is being filled up. The slope tells us how fast the water is being added. The steeper the slope, the faster the rate.
Compare the first time the pool is filled up to the second time we fill it up. The second upward slope is steeper, indicating a faster rate. So this means either we brought a bigger hose, we increased the water flow rate, or we used two valves.
The downhill portion is when the pool is being emptied.
The flat parts are when the pool's water level is not changing. This is likely when the pool is filled to capacity. Of course, there's a buffer between the water level and the deck level, to avoid water spilling onto the deck (since water is going to be splashed and sloshed around).
All of these facts lead to choice B being the answer.
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Extra info:
- Choice A is false because the people in the pool will reduce the water level (splashing moves the water onto the deck) but this amount of water removed is very tiny compared to the massive volume of water in the pool. If choice A was true, then you'd need a hose to constantly be refilling the pool.
- Choice C is false because of the phrasing "immediately after the pool is filled to capacity". This choice of language directly means there wouldn't be any flat part of the graph. Instead we'd have a sharp decline just as we reached the peak.
- Choice D is false because of the fact it mentions the refill rate is the same as the initial fill rate. This is not true because the second increasing portion is steeper compared to the first increasing portion.
So we could effectively eliminate choices A, C and D to be left with B as our final answer.
