Question

Angelina 先以平均 $80$ 千米/小时的速度驾驶，然后停车加油 $20$ 分钟。停车后，她以平均 $100$ 千米/小时的速度驾驶。包括停车时间在内，她总共用 $3$ 小时行驶了 $250$ 千米。下列哪个方程可用来求她停车前驾驶的时间 $t$ ，单位为小时？

Angelina drove at an average rate of $80$ kph and then stopped $20$ minutes for gas. After the stop, she drove at an average rate of $100$ kph. Altogether she drove $250$ km in a total trip time of $3$ hours including the stop. Which equation could be used to solve for the time $t$ in hours that she drove before her stop?

$80t + 100\left(\dfrac83 - t\right) = 250$

$80t = 250$

$100t = 250$

$90t = 250$

$80\left(\dfrac83 - t\right) + 100t = 250$

答案：A

知识点：路程、速度与时间一次方程

难度评级：1370

解答：

停车前，Angelina 行驶了 $80t$ 千米。

停车用时 $\frac{1}{3}$ 小时，所以总驾驶时间为 $3-\frac13=\frac83$ 小时；停车后她驾驶 $\frac83-t$ 小时，行驶 $100\left(\frac83-t\right)$ 千米。

因此方程为 $80t+100\left(\frac83-t\right)=250$ 。

所以正确答案是 A。

Before the stop, Angelina drove $80t$ km.

The stop takes $\frac{1}{3}$ of an hour, so her total driving time is $3-\frac13=\frac83$ hours. After the stop, she drives for $\frac83-t$ hours, covering $100\left(\frac83-t\right)$ km.

The total distance equation is $80t+100\left(\frac83-t\right)=250.$

Thus, A is the correct answer.

2010 AMC 10A 第 13 题

答案：A

难度评级：1370

解答：

其他年份的第 13 题