【数学讨论稿】十月溯雪讨论稿101-200 11月1日订正版更新！

hahajiao

127题，条件1不是应该推出a比-1大，比1小吗？虽然还是sufficient，但是结果不一样吧~

hahajiao

134题，最小的range不应该是240吗？

1999年的range是240，所以不可能是数学君说的最小是0的情况~最小也已经有240了~~然后，只要2000年的这个月营业额320是在1999年营业额的range之内的话，这个range就不会增加，所以还是240

hahajiao

41238635 发表于 2015-11-11 11:58
各位大神 134题那个什么range的根本看不懂啊 求解答 最小的话240不是更小吗

同意~我也觉得是240~

hahajiao

请问，题目里面求问X是不是大于0，结果两个条件一起可以推导出x小于0，那应该选C（条件充分可以判断）还是选E（条件充分判断出结论不成立）呢？

147852gmat

hahajiao 发表于 2015-11-12 20:58
134题，最小的range不应该是240吗？

1999年的range是240，所以不可能是数学君说的最小是0的情况~最小也已 ...

let's assume
Year 1999, X1= smallest revenue, Y1 = largest revenue
Year 2000, X2= smallest revenue, Y2= largest revenue

X1-Y1=240
X2-Y2=320

the smallest possible range is when X1 and Y1 are in between X2 Y2, since it's impossible for X2 Y2 to be in between X1 Y2.

For instance, X1=760 Y1 =1000
For Y2 to be in the range of 760 and 1000, Y2 has to be smaller than 1000 and X2 be larger than 760. then if Y2 is 999, X2 will be 679. You can see that X2 can never be larger than 760 if Y2 is smaller than 1000, Vise versa...

147852gmat

hahajiao 发表于 2015-11-12 20:16
请问126有思路分析吗？现在好像就一个答案，不太理解为什么~

since we know that the sheet has L=6 W=1....if you want to wrap the cubic using this sheet...it's obvious that any cubic having s>1 is impossible to wrap, so the largest has to be  1*1*1=1 feet^3

147852gmat

dophinkk 发表于 2015-11-12 14:14
172题，我怎么算到N=11？

n! = 2^(11)* 5^(2) *k , k doesn't contain any 2 or 5 as factors

2^1 , 4=2^2, 6=2*3, 8=2^3, 10=2*5 ( up to 11, there are 8 2s), 12= 2^2 * 3, 14= 2*7 (in total of 11 2s)

5= 5^1, 10=5*2 (in total of 2)

so...the answer is 14

147852gmat

frozen_17 发表于 2015-11-12 18:27
为什么109题我算出来余数是1.。。。。。。。。。。。。。。。。。。。。啊！！！！！！ ...

V1
7^548/10，余数是

Unit digit will always be 7,9,3,1
548/4=137 ...then you know 7^548 ends with 1, then divided by 10, the remainder is 1

V2
by XU.Arno
问 7 的 584 次方除以 10 的余数,因为是有 V2 规律,793179317 所以很方便答
出来

584/4=146, same as V1...remainder is 1

V3 求 7^538 的余数(就是 7 的余数是 7.。7^2 ,7^3,7^4,这四个为一组余数开始循环,答案是 7)

538/4=134, the unit digit 9... then is remainder is 9 if divided by 10

hahajiao

147852gmat 发表于 2015-11-12 23:04
let's assume
Year 1999, X1= smallest revenue, Y1 = largest revenue
Year 2000, X2= smallest revenu ...

I think the major difference between you and I are not our logical thinking, but the understanding of the conditions given.

you read that the range for year 2000 is 320, but I thought that one figure of the monthly revenue in year 2000 is 320.

Thanks for the detailed explanation. Really appreciate!

hahajiao

147852gmat 发表于 2015-11-12 23:30
since we know that the sheet has L=6 W=1....if you want to wrap the cubic using this sheet...it's  ...

so”包起“ does not mean the sheet need to cover all the 6 dimensions of the cubic? Coz in that case, the largest may need to be less than 1.