Question

Brenda 和 Sally 从圆形跑道上一对直径相对的点出发，沿相反方向跑。她们第一次相遇时 Brenda 跑了 $100$ 米。下一次相遇时，Sally 已经从第一次相遇点又跑了 $150$ 米。两人都以恒定速度跑。跑道长多少米？

Brenda and Sally run in opposite directions on a circular track, starting at diametrically opposite points. They first meet after Brenda has run $100$ meters. They next meet after Sally has run $150$ meters past their first meeting point. Each girl runs at a constant speed. What is the length of the track in meters?

$250$

$300$

$350$

$400$

$500$

答案：C

知识点：相对速度路程、速度与时间比与比例

难度评级：1540

解答：

第一次相遇前，两人合计跑了半圈。两次相遇之间，两人合计跑了一整圈，是前一段总路程的两倍，所以 Brenda 在这段中跑了 $2 \cdot 100 = 200$ 米。

Sally 在同一段中跑了 $150$ 米，所以跑道全长为 $200 + 150 = 350.$

所以正确答案是 C。

Before the first meeting the two together cover half the track. Between the first and second meetings they together cover a full track, which is twice as far, so Brenda runs $2 \cdot 100 = 200$ meters in that stretch.

Sally runs $150$ meters in the same stretch, so the full track length is $200 + 150 = 350.$

Thus, the correct answer is C.

2004 AMC 10A 第 17 题

答案：C

难度评级：1540

解答：

其他年份的第 17 题