TT的逻辑，来源－CAT模考,谢谢

terry_tin · 发表于 2003-5-25 19:29:00

No. 1
A chemist knows the following about the colorless liguid in a certain beaker
1. If chemical X is added to the liquid, it will turn red
2. If chemical Y is added to the liquid, it will turn Blue
3. if both chemical x and chemical y is added to the liquid, it will turn green
Given the statements in the reading, which of the following must be true?
A. If the liquid remained colorless, then no chemicals were added
B. If the liquid rurned green, then both chmical x and chmical y were added
C. if the liquid turned blue, then chemical x was not added
D if the liquid turned blue, then it is possible that chemical y was added
E. if the liquied remained colorless, then it is possible that chemical x and only chemical x was added
The anwser is D. 我选的是C, 我觉得C是原命题1的逆否命题
原命题： If chemical X is added to the liquid, it will turn red
逆否命题：turn blue(not turn red)--->Chemical x is not added.
为什么这个选项不正确呢？
谢谢

lyricling · 发表于 2003-5-25 20:16:00

我觉得CD都有可能。
C项虽是条件1的逆否命题，但它是否会与条件3矛盾呢？因为条件3说了这样一种可能，如果X与其它东西一起加入，颜色可能会不是红色。所以当它是蓝色时，有可能X与别的东西同时存在。
D项有一个possible，这个词的存在，表明D项并没有将条件2的逆命题视作充分条件，Y当然有可能存在。
不过我觉得这样的解释有些牵强，再想下去有点钻牛角尖。不知哪位高手有更高明的看法？
不过我觉得，真正的考试不会有这样的情况出现吧。

renprince · 发表于 2003-5-25 21:21:00

首先这是什么CAT上面的呢？感觉怪异的思路

另外记住：turn blue(not turn red)
turn blue 的逆命题是not turn blue
所以推不出

[此贴子已经被作者于2003-5-25 21:22:25编辑过]

siebel · 发表于 2003-5-25 21:27:00

原命：只加X，变red。
妮否：没变red，不只加了X。

[此贴子已经被作者于2003-5-25 21:30:59编辑过]

albert · 发表于 2003-5-25 22:08:00

以下是引用terry_tin在2003-5-25 19:29:00的发言：
No. 1
A chemist knows the following about the colorless liguid in a certain beaker
1. If chemical X is added to the liquid, it will turn red
2. If chemical Y is added to the liquid, it will turn Blue
3. if both chemical x and chemical y is added to the liquid, it will turn green
Given the statements in the reading, which of the following must be true?
A. If the liquid remained colorless, then no chemicals were added
B. If the liquid rurned green, then both chmical x and chmical y were added
C. if the liquid turned blue, then chemical x was not added
D if the liquid turned blue, then it is possible that chemical y was added
E. if the liquied remained colorless, then it is possible that chemical x and only chemical x was added
The anwser is D. 我选的是C, 我觉得C是原命题1的逆否命题
原命题： If chemical X is added to the liquid, it will turn red
逆否命题：turn blue(not turn red)--->Chemical x is not added.
为什么这个选项不正确呢？
谢谢

其实看一下原题条件3就知道C是错的。
原题： If chemical X is added to the liquid, it will turn red(意思是只加X)
逆否： not turn red -> only chemica X is added to the liquid is not true...
结论有两可能： 1 X根本没加l 2 X加了，可是不是ONLY，another chemical
must be added into

TT的逻辑，来源－CAT模考,谢谢

TT的逻辑，来源－CAT模考,谢谢

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