In a store room, one group of staff members fill the store with boxes and the other group of staff take the boxes from the store and supply them to the market

题目

In a store room, one group of staff members fill the store with boxes and the other group of staff take the boxes from the store and supply them to the market. The boxes are stored at the rate of 5 boxes per hour whereas they are supplied at the rate of 3 boxes per hour. If the room is filled with 60 boxes, in how many hours it will be filled?

选项

20 hours

30 hours

50 hours

80 hours

120 hours

解析

这个房间的总容量为 \(\frac{x}{4}=60\)，因此 \(x=240\)。我们需要将房间填充至其容量的 \(\frac{2}{3}\)，这意味着 \[ \frac{2}{3} \times 240 = 160 \text{ 个箱子} \] 我们每小时存放5个箱子，同时每小时会运入3个箱子，因此**每小时净存放**的箱子数量为2个。房间里已经有60个箱子，还需要额外存放100个箱子（因为总共需要存放160个箱子）。以每小时2个箱子的净存放速度，我们需要50小时来存放额外的100个箱子。所以选项C是正确答案。

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