Question

温度每升高 $3^\circ$ ，某种气体的体积就膨胀 $4$ 立方厘米。如果温度为 $32^\circ$ 时气体体积是 $24$ 立方厘米，那么温度为 $20^\circ$ 时气体体积是多少立方厘米？

For every $3^\circ$ rise in temperature, the volume of a certain gas expands by $4$ cubic centimeters. If the volume of the gas is $24$ cubic centimeters when the temperature is $32^\circ,$ what was the volume of the gas in cubic centimeters when the temperature was $20^\circ?$

$8$

$12$

$15$

$16$

$40$

答案：A

知识点：速率逆推法

难度评级：950

解答：

从 $32^\circ$ 到 $20^\circ$ 是下降 $12^\circ$ ，也就是 $4$ 个 $3^\circ$ 。

体积减少 $4 \times 4 = 16$ 立方厘米，所以从 $24$ 降到 $24 - 16 = 8$ 。

所以正确答案是 A。

From $32^\circ$ to $20^\circ$ is a $12^\circ$ decrease, which is $4$ steps of $3^\circ.$

The volume decreases by $4 \times 4 = 16$ cubic centimeters, from $24$ down to $24 - 16 = 8.$

Thus, the correct answer is A .

1991 AMC 8 第 21 题

答案：A

难度评级：950

解答：

其他年份的第 21 题