2021 AMC 10A Fall 第 2 题

Question

Menkara 有一张

4 \times 6

的索引卡片。若她把这张卡片的一边长度缩短

1

英寸，卡片面积会变成

18

平方英寸。如果她改为把另一边长度缩短

1

英寸，那么卡片面积是多少平方英寸？

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

先判断缩短哪一边会得到面积

18

。

Figure out which side was shortened to get area

18

然后改为缩短另一边。

Then shorten the other side instead

若把

4

英寸的一边缩短

1

英寸，就得到

3\times 6

的卡片，面积为

18

平方英寸。

因此题中原先缩短的是

4

英寸的一边。若改为缩短另一边，则得到

4\times 5

的卡片，面积为

20

。

所以正确答案是 E。

If she shortens the

4

-inch side by

1,

she has a

3\times 6

card, whose area is

18

square inches.

Therefore the given shortening was on the

4

-inch side. Shortening the other side instead gives a

4\times 5

card, with area

20

square inches.

Thus, E is the correct answer.

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