2017 AMC 10B 第 7 题

Question

Samia 骑自行车去拜访朋友，平均速度为每小时

17

千米。当她走完到朋友家的路程的一半时，轮胎漏气了，于是她以每小时

5

千米的速度走完剩下的一半路程。

她总共花了

44

分钟到达朋友家。四舍五入到最接近的十分之一千米，Samia 走了多远？

Samia set off on her bicycle to visit her friend, traveling at an average speed of

17

kilometers per hour. When she had gone half the distance to her friend’s house, a tire went flat, and she walked the rest of the way at

5

kilometers per hour.

In all, it took her

44

minutes to reach her friend’s house. In kilometers rounded to the nearest tenth, how far did Samia walk?

2.0

2.2

2.8

3.4

4.4

设她步行的距离为

d

，则骑车距离也是

d

。

Let the walking distance be

d

, so the biking distance is also

d

骑车时间加步行时间等于

44

分钟。

Add the biking time and walking time to get

44

minutes

设

d

为 Samia 步行的距离。她骑车走过的距离与此相同，所以由总用时可得

\dfrac{d}{17}+\dfrac{d}{5}=\dfrac{44}{60}\text{。}

解得

d=\dfrac{17}{6}=2.833\ldots

，四舍五入到十分位约为

2.8

千米。

所以正确答案是 C。

Let

d

be the distance Samia walked. She bicycled the same distance, so her total travel time gives

\dfrac{d}{17}+\dfrac{d}{5}=\dfrac{44}{60}.

Solving yields

d=\dfrac{17}{6}=2.833\ldots,

which rounds to

2.8

kilometers.

Thus, the correct answer is C .

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