Question

Jack 和 Jill 要去离家一英里的游泳池游泳。他们同时离家。Jill 以每小时 $10$ 英里的恒定速度骑自行车去游泳池。Jack 以每小时 $4$ 英里的恒定速度步行去游泳池。Jill 比 Jack 早到多少分钟？

Jack and Jill are going swimming at a pool that is one mile from their house. They leave home simultaneously. Jill rides her bicycle to the pool at a constant speed of $10$ miles per hour. Jack walks to the pool at a constant speed of $4$ miles per hour. How many minutes before Jack does Jill arrive?

$5$

$6$

$8$

$9$

$10$

答案：D

知识点：路程、速度与时间

难度评级：660

视频讲解：

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文字解答：

Jack 的速度是 $4$ 英里每 $60$ 分钟，所以他到游泳池需要 $\dfrac{60}{4} = 15$ 分钟。

Jill 的速度是 $10$ 英里每 $60$ 分钟，所以她到游泳池需要 $\dfrac{60}{10} = 6$ 分钟。

两人的时间差为 $15-6 = 9$ 分钟。

所以正确答案是 D。

Jack travels at a rate of $4$ miles per $60$ minutes. Therefore, it takes him $\dfrac{60}{4} = 15$ minutes to get to the pool.

Jill travels at a rate of $10$ miles per $60$ minutes. Therefore it takes her $\dfrac{60}{10} = 6$ minutes to get to the pool.

Therefore, the difference in their times is $15-6 = 9$ minutes.

Thus, the correct answer is D .

2015 AMC 8 第 3 题

答案：D

难度评级：660

视频讲解：

文字解答：

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