Question

Menkara 有一张 $4 \times 6$ 的索引卡片。如果她把这张卡片的一边长度缩短 $1$ 英寸，卡片的面积会变成 $18$ 平方英寸。如果她改为把另一边的长度缩短 $1$ 英寸，卡片的面积会是多少平方英寸？

Menkara has a $4 \times 6$ index card. If she shortens the length of one side of this card by $1$ inch, the card would have area $18$ square inches. What would the area of the card be in square inches if instead she shortens the length of the other side by $1$ inch?

$16$

$17$

$18$

$19$

$20$

答案：E

知识点：矩形面积

难度评级：1020

解答：

原卡片是 $4 \times 6$ 。把一边缩短 $1$ 英寸后面积为 $18$ ，必须是 $3 \times 6 = 18$ ，所以被缩短的是 $4$ 英寸的边。

若改为把另一边缩短 $1$ 英寸，则面积为 $4 \times 5 = 20$ 平方英寸。

所以正确答案是 E。

The original card is $4 \times 6.$ Shortening a side by $1$ inch gives area $18,$ which requires $3 \times 6 = 18,$ so the reduced side was the $4$ -inch side.

Shortening the other side by $1$ inch instead gives $4 \times 5 = 20$ square inches.

Thus, the correct answer is E.

2021 AMC 12A Fall 第 2 题

答案：E

难度评级：1020

解答：

其他年份的第 2 题