Question

Anh 去海滩旅行时，在高速公路上行驶了五十英里，在海边通道上行驶了十英里。他在高速公路上的速度是海边通道上的三倍。如果 Anh 在海边通道上开了三十分钟，那么他的整趟行程用了多少分钟？

On a trip to the beach, Anh traveled 50 miles on the highway and 10 miles on a coastal access road. He drove three times as fast on the highway as on the coastal road. If Anh spent 30 minutes driving on the coastal road, how many minutes did his entire trip take?

$50$

$70$

$80$

$90$

$100$

答案：C

知识点：路程、速度与时间单位换算

难度评级：900

视频讲解：

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文字解答：

Anh 在海边通道上开了 $10$ 英里，用了 $30$ 分钟。因此海边通道速度（记为 $v_c$ ）是也就是每分钟 $\dfrac13$ 英里。因为他在高速公路上的速度是 $3$ 倍，也就是 $v_h=3v_c$ ，所以高速公路速度为英里每分钟。他在海边通道上开了 $30$ 分钟，在高速公路上开了 $50$ 英里，速度为每分钟 $1$ 英里，所以这 $50$ 英里需要 $50$ 分钟。 $\begin{align*}v_c&=\dfrac{10}{30}\\ &=\dfrac13.\end{align*}$ $3\cdot \dfrac13 = 1$

因此总行程时间为 $50+30=80$ 分钟。

所以正确答案是 C。

Anh drove $10$ miles on the coastal road in $30$ minutes. Therefore, his speed on the coastal road (notated as $v_c$ ) is $\begin{align*}v_c&=\dfrac{10}{30}\\ &=\dfrac13.\end{align*}$ This is $\dfrac13$ mile per minute. Since he drives $3$ times as fast on the highway (i.e. $v_h=3v_c$ ), his highway speed is $3\cdot \dfrac13 = 1$ mile per minute. Armed with these two facts, we know that Anh drove for $30$ minutes on the coastal road, and he drove $50$ miles at $1$ mile per minute. This means it takes $50$ minutes to drive the $50$ miles on the highway.

As such, the total travel time is $50+30=80$ minutes.

Thus, the correct answer is C.

2018 AMC 8 第 6 题

答案：C

难度评级：900

视频讲解：

文字解答：

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