Question

Homer 开始以每分钟削 $3$ 个土豆的速度削一堆 $44$ 个土豆。四分钟后 Christen 加入，以每分钟削 $5$ 个土豆的速度削。完成时，Christen 削了多少个土豆？

Homer began peeling a pile of $44$ potatoes at the rate of $3$ potatoes per minute. Four minutes later Christen joined him and peeled at the rate of $5$ potatoes per minute. When they finished, how many potatoes had Christen peeled?

$20$

$24$

$32$

$33$

$40$

答案：A

知识点：速率

难度评级：1290

解答：

Christen 加入时，Homer 已经削了 $3 \cdot 4 = 12$ 个土豆，还剩 $44 - 12 = 32$ 个。

Homer 和 Christen 合起来每分钟削 $5 + 3 = 8$ 个土豆，因此还需要 $32 \div 8 = 4$ 分钟削完剩下的。

$4$ 分钟内，Christen 削了 $4 \cdot 5 = 20$ 个土豆。

所以正确答案是 A。

Homer had peeled $3 \cdot 4 = 12$ potatoes by the time Christen joined him, leaving $44 - 12 = 32$ potatoes.

Together, Homer and Christen peel $5 + 3 = 8$ potatoes per minute, taking them $32 \div 8 = 4$ minutes to peel the rest.

In $4$ minutes, Christen peeled $4 \cdot 5 = 20$ potatoes.

Thus, A is the correct answer.

2001 AMC 8 第 15 题

答案：A

难度评级：1290

解答：

其他年份的第 15 题