PrepDS第一部分做完，有几道题搞不懂

dontwannalose

18. What is the hundredths digit of the decimal z ?
(1) The tenths digit of 100z is 2.
(2) The units digit of 1,000z is 2.
这体完全搞不动100后的Z是什么意思，是100*z or 100.Z????? （答案D)

169.  If the integers a and n are greater than 1 and the product of the first 8 positive integers is a multiple of a^n, what is the value of a ?
(1) a^n = 64
(2) n = 6
这题答案是B,但我觉得它是错的：n等于6并没有确定a的取值

200. Of the 1,000 companies responding to a certain survey, what percent indicated that they had a business recovery plan?
(1) 200 of the companies did not indicate that they had a business recovery plan.
(2) The number of companies that indicated that they had a business recovery plan was 4 times the number that did not indicate that they had a business recovery plan.
此题答案是D,但是题目只是说responding,弃权即不选也是respondng 的一种，不是吗？

203. What is the remainder when the positive integer x is divided by 6?
(1) When x is divided by 2, the remainder is 1; and when x is divided by 3, the remainder is 0.
(2) When x is divided by 12, the remainder is 3.
这题完全不知如何下手（答案是D)

214.The cost of a square slab is proportional to its thickness and also proportional to the square of its length. What is the cost of a square slab that is 3 meters long and 0.1 meter thick?
(1) The cost of a square slab that is 2 meters long and 0.2 meter thick is $160 more than the cost of a square slab that is 2 meters long and 0.1 meter thick.
(2) The cost of a square slab that is 3 meters long and 0.1 meter thick is $200 more than the cost of a square slab that is 2 meters long and 0.1 meter thick.
此题答案同样是D,但我觉得是E. 就第一条信息来说，因为slab同时与长度的平方和厚度成比例关系（题目中并没有假设这两种比例是否相等）而该信息并没有给出长度平方（square of length) 的比例关系,所以我觉得应该算不出答案

求指点

kingapple25

203题

条件一：可得通项为X= 6k+3
条件二：通项为x=12k+3
所以两个都能确定除以6的余数

dontwannalose

and to kingapple25, am really appreciate ur answers

kingapple25

关于弃权即不选是不是respondng 的一种，我持保留态度，不过我更倾向于不是，呵呵，弃权应该算是没有responding吧

dontwannalose

http://forum.chasedream.com/GMAT_Preparation/thread-366848-1-1.html
prep数学详解下载

-- by 会员 free_over (2010/2/11 23:28:00)

那个资料我有，但是相关题的解释我不是看不懂就是不同意它的解法
thx a lot anyway

kingapple25

169题的话，我想是因为a^n是1-8的乘积的因子，而1-8的乘积可以写成2^7*3^2*5*7的形式，那么如果指数n要等于6，底数a就只能等于2了，不然做不成因子

free_over

http://forum.chasedream.com/GMAT_Preparation/thread-366848-1-1.html
prep数学详解下载

kingapple25

18. What is the hundredths digit of the decimal z ?
(1) The tenths digit of 100z is 2.
(2) The units digit of 1,000z is 2.
这体完全搞不动100后的Z是什么意思，是100*z or 100.Z????? （答案D)

这里的100z就是100*z,其中z是一个小数