Question

Cheenu 小时候能在 $3$ 小时 $30$ 分钟内跑 $15$ 英里。现在他年老了，能在 $4$ 小时内走 $10$ 英里。现在他走一英里比小时候跑一英里多花多少分钟？

When Cheenu was a boy he could run $15$ miles in $3$ hours and $30$ minutes. As an old man he can now walk $10$ miles in $4$ hours. How many minutes longer does it take for him to walk a mile now compared to when he was a boy?

$6$

$10$

$15$

$18$

$30$

答案：B

知识点：速率单位换算

难度评级：720

视频讲解：

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文字解答：

为了更容易比较速度，将它们都换成每英里所需分钟数。

小时候他跑 $15$ 英里用了 $3 \cdot 60 + 30 = 210$ 分钟，所以速度为 $210 / 15 = 14$ 分钟每英里。

现在他走 $10$ 英里用了 $4 \cdot 60 = 240$ 分钟，所以速度为 $240 / 10 = 24$ 分钟每英里。

相减得，现在他走一英里多花 $10$ 分钟。

所以正确答案是 B。

To better compare the rates, we can change his speed into minutes per mile.

As a boy he ran $15$ miles in $3 \cdot 60 + 30 = 210$ minutes, which means that he ran at a pace of $210 / 15 = 14$ minutes per mile.

As an adult, he can walk $10$ miles in $4 \cdot 60 = 240$ minutes, which means he walks at a pace of $240 / 10 = 24$ minutes per mile.

Subtracting the two, we get that he takes $10$ more minutes to walk a mile as an adult.

Thus, B is the correct answer.

2016 AMC 8 第 4 题

答案：B

难度评级：720

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文字解答：

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