2006 AMC 12A 第 14 题

先试着解答 2006 AMC 12A 第 14 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 2006 AMC 12A 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。

14.

两位农民约定猪价值 $300\$300,山羊价值 $210\$210。当一位农民欠另一位钱时,他用猪或山羊偿债,并可根据需要以山羊或猪的形式找零。(例如,一笔 $390\$390 的债可以用两头猪支付,并收到一只山羊作找零。)能用这种方式结清的最小正债务金额是多少?
Two farmers agree that pigs are worth $300\$300 and that goats are worth $210.\$210. When one farmer owes the other money, he pays the debt in pigs or goats, with “change” received in the form of goats or pigs as necessary. (For example, a $390\$390 debt could be paid with two pigs, with one goat received in change.) What is the amount of the smallest positive debt that can be resolved in this way?
$5\$5
$10\$10
$30\$30
$90\$90
$210\$210
答案:C
知识点:最大公约数丢番图方程
小提示:
可结清的债务形如 300p+210g300p + 210g,其中 p,gp, g 为整数。
A resolvable debt has the form 300p+210g300p + 210g for integers p,gp, g
大提示:
每个这样的值都是 gcd⁡(300,210)\gcd(300, 210) 的倍数。
Every such value is a multiple of gcd⁡(300,210)\gcd(300, 210)
解答:
债务 DD 能结清当且仅当 D=300p+210gD = 300p + 210g =30(10p+7g)= 30(10p + 7g),其中 p,gp, g 为整数。因此 DD 是 gcd⁡(300,210)=30\gcd(300, 210) = 30 的倍数,所以没有更小的正债务可行。
$30\$30 的债务可以做到,因为 30=300(−2)+210(3)30 = 300(-2) + 210(3),即给出 33 只山羊并收到 22 头猪作为找零。
因此,正确答案是 C。
A debt DD is resolvable if and only if D=300p+210gD = 300p + 210g =30(10p+7g)= 30(10p + 7g) for integers p,g.p, g. Thus DD is a multiple of gcd⁡(300,210)=30,\gcd(300, 210) = 30, so no smaller positive debt works.
A debt of $30\$30 is achievable since 30=300(−2)+210(3),30 = 300(-2) + 210(3), i.e. give 33 goats and receive 22 pigs in change.
Thus, the correct answer is C.
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