gwd21-20: Of the 60 animals on a certain 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.
答案为C，为何A 不对？有题干可得40 只pigs or cows, 结合（1）可得这40 只能是cow, 若是40只pigs, cows 将是80只，而题干只有60 animals. 请nn 解惑。
模拟题：If xy=1, what is the value of [2(x+y)^2]/[2(x-y)^2] ?
a. 2 b.4 c.8 d.16 e.32
答案为d.该题无从下手，请nn 指教。先谢了。
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第一题理解有误。不是猪就是牛，就是说那2/3，就是40个，里面猪牛都有。由1，牛比猪的2倍多，就是说牛大于2*40/3=26.67头，猪小于13.33头。条件2确定猪〉12，则猪为13
第二题有讨论过。我的意见是题目有问题。2约掉，平方合并，就算(x+y)/(x-y)，把x=1/y带入(1+y^2)/(1-y^2)，由于y取值的任意性可知本题应有多个答案，所以我认为有问题
oh, I see for the 1st one.
The 2nd one, I agree with you.
Thanks for your help, Charmant!
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发表于 2005-11-14 04:05:00
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