求助几道数学题

rainny0906

1、fi X4+y4=100,then the greater possble value of X is between
0 and 3(my choice)   3and 6(correct answer)

2、at a dinner party,5 persons are to be seated around a circular table.two seating arrangements are considered different only when the positions of the people are different relative to each other. what is the total number of different possible seating arrangements for the group.
10(my choice)    24(correct answer)

3、if there are more than two numbers in a certain list,is each  of the number in the list equal to 0?
(1)the product of any two numbers in the list is equal to 0
(2)the sum of any two numbers in the list is equal to 0

each statement alone is sufficient (my choice)
statement(2)alone is sufficient,but (1)alone is not sufficient(correct answer)

4、of the 60 animals on a farm,2/3 are either pigs or cows,how many of the animals are cows?
(1)the farm has more than twice as many cows as it has pigs
(2)the farm has more than 12 pigs
statement(1)alone is sufficient,but (2)alone is not sufficient(my choice)
both statements together are sufficient,but neither alone is sufficient.(correct answer)

求助各位DCers，我的答案与正确答案差太多，请各位帮我分析一下。
多谢啦

zxl6300

今天也在“2/3 are either cows or pigs”纠结了半天，在网上查询了之后，发现Manhattan上有人解释了一下为什么这里的“either...or...”就相当于“and”，摘录如下（地址：https://www.manhattanprep.com/gmat/forums/of-the-60-animals-on-a-certain-farm-2-3-are-either-cows-or-t3417.html）：

“the statement "2/3 are either cows or pigs" doesn't mean that there are either 40 cows or 40 pigs. it means that, if you take the cows and the pigs together, they constitute 2/3 of the animals on the farm.
in other words, cows + pigs = 40.
(i can understand your alternate reading of the problem statement; it's reasonable enough. just remember that the gmat is their playground, not yours, and so you have to play by their rules - so remember the way certain statements are written. as a postscript, i hope that future problems like this one will be purged and/or rewritten for clarity before they make it into the official question pool; it would be a shame if students miss the problem just because of its ambiguity.) ”

katy2230

bunnyjessie 发表于 2017-11-7 15:16
Mark一下！

Mark一下！               

bunnyjessie

莫二 发表于 2012-9-4 14:28
其实我是纠结于翻译理解啊，为什么X+Y=40,这里这个“2/3 are either pigs or cows"不是说猪有40只或者牛有4 ...

Mark一下！               

bunnyjessie

agnesliu 发表于 2010-8-4 15:48
第2题我也碰到了，而且是两次，两次都错，看到1楼的解答，总算明白了

在Gmat里either 你就理解成并集的意思，所以这里是指牛和猪一共40哦

莫二

其实我是纠结于翻译理解啊，为什么X+Y=40,这里这个“2/3 are either pigs or cows"不是说猪有40只或者牛有40只吗？

agnesliu

第2题我也碰到了，而且是两次，两次都错，看到1楼的解答，总算明白了

eflet222

第3题补充一下广义证明:
由x1+x2=x1+x3=...=x1+xn=0......(1)
得到x2=x3=...=xn
又x2+x3=0所以x4=x5=...=xn=x2=x3=0
代入(1)式得x1=0
所以都等于0得证

miller811

LZ的分析很详细，多谢啦

-- by 会员 rainny0906 (2010/8/2 10:24:45)

你这LZ当的。。。。

rainny0906

LZ的分析很详细，多谢啦