1958 AMC 12 第 45 题

先试着解答 1958 AMC 12 第 45 题,然后核对你的答案与精心整理的解答,解答来自 LIVE by Po-Shen Loh。你也可以参加完整限时模拟考试、查看全部 1958 AMC 12 解答,或核对答案。

所有题目均经美国数学协会(MAA)官方合法授权使用。

45.

一张支票的金额为 xx 美元 yy 美分,其中 xx 和 yy 都是两位数。误兑为 yy 美元 xx 美分,错误金额比正确金额多 $17.82\$17.82。则:
A check is written for xx dollars and yy cents, xx and yy both two-digit numbers. In error it is cashed for yy dollars and xx cents, the incorrect amount exceeding the correct amount by $17.82.\$17.82. Then:
xx 不可能大于 7070
xx cannot exceed 7070
yy 可以等于 2x2x
yy can equal 2x2x
支票金额不可能是 55 的倍数
the amount of the check cannot be a multiple of 55
错误金额可以等于正确金额的两倍
the incorrect amount can equal twice the correct amount
正确金额各位数字之和能被 99 整除
the sum of the digits of the correct amount is divisible by 99
答案:B
知识点:钱币数字一次方程
小提示:
将正确金额和错误金额都写成美分
Write the correct and incorrect amounts in cents
大提示:
两者之差化简为 99(y−x)99(y-x)
Their difference simplifies to 99(y−x)99(y-x)
解答:
以美分计,错误金额减正确金额为 (100y+x)−(100x+y)=99(y−x)。 \begin{aligned} &(100y+x)-(100x+y)\\ &\qquad=99(y-x) \end{aligned}\text{。}由于 $17.82\$17.82 等于 17821782 美分,99(y−x)=1782, 99(y-x)=1782\text{,}所以 y−x=18y-x=18。两位数 x=18, y=36x=18,\ y=36 满足此关系,并且 y=2xy=2x。因此这种相等关系可以发生。
所以正确答案为 B。
In cents, the incorrect amount minus the correct amount is (100y+x)−(100x+y)=99(y−x). \begin{aligned} &(100y+x)-(100x+y)\\ &\qquad=99(y-x). \end{aligned} Since $17.82\$17.82 is 17821782 cents, 99(y−x)=1782, 99(y-x)=1782, so y−x=18.y-x=18. The two-digit values x=18, y=36x=18,\ y=36 satisfy this relation and have y=2x.y=2x. Thus that equality can occur.
Therefore, the correct answer is B.
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