2017 AMC 8 第 23 题

先试着解答 2017 AMC 8 第 23 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 2017 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。

23.

连续四天,琳达每天旅行一小时,并且她的速度使她每行进一英里所需分钟数都是整数。第一天之后,每天她的速度都降低,使得每行进一英里所需分钟数比前一天多 55 分钟。四天中每天她行进的距离也都是整数英里。这四次旅行一共多少英里?
Each day for four days, Linda traveled for one hour at a speed that resulted in her traveling one mile in an integer number of minutes. Each day after the first, her speed decreased so that the number of minutes to travel one mile increased by 55 minutes over the preceding day. Each of the four days, her distance traveled was also an integer number of miles. What was the total number of miles for the four trips?
1010
1515
2525
5050
8282
答案:C
知识点:因数等差数列
小提示:
每天每英里所需分钟数必须整除 6060
Each day’s minutes per mile must divide 6060.
大提示:
列出 6060 的因数,并找出四个相差 55 的因数
List the divisors of 6060 and find four of them spaced 55 apart.
视频讲解:
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文字解答:
琳达每天旅行 6060 分钟。因为每天每英里所需分钟数是整数,且每天行进英里数也是整数,所以每天的每英里分钟数必须是 6060 的因数。6060 的因数为 11、22、33、44、55、66、1010、1212、1515、2020、3030 和 6060。其中唯一一组四个相邻相差 55 的数是 55、1010、1515 和 2020。四天总路程为 605+6010+6015+6020=25 \dfrac{60}{5} + \dfrac{60}{10} + \dfrac{60}{15} + \dfrac{60}{20} = 25 英里。
所以正确答案是 C。
Linda traveled for 6060 minutes every day. Since one mile was traveled in an integer amount of minutes each day, her minutes per mile every day must be a factor of 60.60. The factors of 6060 are 1,1, 2,2, 3,3, 4,4, 5,5, 6,6, 10,10, 12,12, 15,15, 20,20, 30,30, and 60.60. The only sequence of four of these numbers that differ by 55 are 5,5, 10,10, 15,15, and 20.20. For the four days, she traveled 605+6010+6015+6020=25 \dfrac{60}{5} + \dfrac{60}{10} + \dfrac{60}{15} + \dfrac{60}{20} = 25 miles in total.
Thus, C is the correct answer.
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