2025 AMC 8 第 6 题

先试着解答 2025 AMC 8 第 6 题,然后核对你的答案与视频与精心整理的解答,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 2025 AMC 8 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。

6.

Sekou 写下 1515、1616、1717、1818、1919。擦掉其中一个数后,剩下四个数的和是 44 的倍数。他擦掉了哪个数?
Sekou writes the numbers 15,15, 16,16, 17,17, 18,18, 19.19. After he erases one of the numbers, the sum of the remaining four numbers is a multiple of 4.4. Which number did he erase?
1515
1616
1717
1818
1919
答案:C
知识点:模运算整除性
小提示:
比较擦掉前后的总和模 44 的余数
Compare the total sum modulo 44 before and after erasing
大提示:
被擦掉的数必须与原总和有相同的模四余数
The erased number must have the same remainder as the original total
视频讲解:
解答视频缩略图
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文字解答:
这五个数除以 44 的余数分别为 33、00、11、22、33。因此五个数的总和模 44 与 3+0+1+2+3=93 + 0 + 1 + 2 + 3 = 9 相同,余数为 11(模 44)。要擦掉一个数后使总和余 00(模 44),必须擦掉一个余数为 11(模 44)的数,也就是 1717。所以答案是 C。
The remainders of the five numbers after dividing by 44 are: 3,3, 0,0, 1,1, 2,2, and 3.3. So, the sum of all five numbers modulo 44 is the same as 3+0+1+2+3=93 + 0 + 1 + 2 + 3 = 9 which has remainder 11 modulo 4.4. Therefore, in order to erase a single number and get a sum that is 00 modulo 4,4, we must erase the number which was 11 modulo 4,4, which was 17.17. Therefore, the answer is C.
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