请教几道GMAT数学~

shain · 发表于 2010-10-19 09:11:12

DS...我怎么觉得余数问题老搞不明白~~
1. If n is a positive integer and r is the remainder when (n-1)(n+1) is devided by 24, what is the value of r?
a. 2 is not a factor of n
b. 3 is not a factor of n

下面两道来自新东方模考题。就是算数，但是计算其都用上了怎么没有一个选项和答案沾边呢~
1. a certain farmer pays $30 per acre per month to rent farmland. how much does the farmer pay per month to rent a rectangular plot of farmland that is 360 feet by 605 feet? (3560 square feet = 1 arce)
a. 5330; b. 3360; c. 1350; d. 360; e. 150

2. How many seconds will it take for a car that is traveling at a constant rate of 45 miles per hour to travel a distance of 22 yards? ( 1 mile = 1160 yards)
a. 8; b. 9; c. 10; d. 11; e. 12

非常感谢！！

zhlee · 发表于 2010-10-19 09:19:22

1 显然不是余数题，选C

如果n不是2的倍数，那么 n-1 和 n+1 都是2的倍数，而且其中之一必然是 4的倍数

如果n不是3的倍数，那么 n-1 和 n+1 中有一个是3的倍数。

在这两个条件下，所以 (n-1)(n+1) 是 24的倍数。也就是说余数是0。

余数题参考我的归纳帖：

http://forum.chasedream.com/GMAT_Math/thread-492064-1-1.html

shain · 发表于 2010-10-19 09:21:29

THANK U!

shain · 发表于 2010-10-19 09:23:32

这个贴貌似是关于余数的~但是貌似2。3不是余数的~厄不好意思~麻烦再帮忙看看第2/3题~谢谢！

zhlee · 发表于 2010-10-19 09:34:39

1. a certain farmer pays $30 per acre per month to rent farmland. how much does the farmer pay per month to rent a rectangular plot of farmland that is 360 feet by 605 feet? (3560 square feet = 1 arce)
a. 5330; b. 3360; c. 1350; d. 360; e. 150

(360*605/3560)*30 一个都不对！

狗狗之后的结果是 —— 大哥你copy past 还带错的， 1 arce 明明是 43560 square feet

(360*605/43560)*30=150

zhlee · 发表于 2010-10-19 09:41:01

2. How many seconds will it take for a car that is traveling at a constant rate of 45 miles per hour to travel a distance of 22 yards? ( 1 mile = 1160 yards)
a. 8; b. 9; c. 10; d. 11; e. 12

45 mph 就是 45*1160/3600 = 14.5 yards per second
22/14.5=1.5 秒

zhlee · 发表于 2010-10-19 09:47:33

去狗狗计算器一查，又是错了

1mile = 1760 yards

45*1760/3600 = 22 yard ，那么就是1秒了。更不对了，还有其他地方错了。

22个yard才多少距离呀，汽车怎么可能要开 8秒 10秒呀？

shain · 发表于 2010-10-20 09:59:18

恩~都怪xdf阿~我举双手发誓我没抄错~他们的模考题害人啊。。。。

谢了~

请教几道GMAT数学~

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