Cracking the LSAT 上的一道题目，为什么感觉有问题？还是我是逻辑白痴－ －

dukesena

2006年版的，上来的ARGUEMENT里ASSMUPTION QUESTION例题2；
 
Beacuse my gas mileage has been steady during the same time period, the alignment of my car's

wheels must be normal.

问ASSMUPTION,
其中一个选项是：

A drop in gas mileage occurs only if a car's wheels are out of alignment.

另外一个是：

Misaligned wheels can sometimes cause a car's mileage to drop.


我上来第一感觉就选了第一个，但是答案说是第二个，解释的不是很明白，望坛子里的各位指点，刚接触LSAT见笑...

poppyxams

我觉得哈，第一个不太对的地方是它把范围限定得不必要的小，就是只有wheels are out of alignment时gas mileage 才出问题，事实上其他故障也可能会导致这个问题，那么如果出问题就无法得出是不是wheels出故障了，但是如果什么问题都没有，那肯定wheels也没问题；第二个恰到好处不浪费，说wheels 故障会导致问题，（不排除其他故障的情况）但是只要什么问题都没有，就说明wheels没问题。

所以可能第二个会稍好一点。

dphxmg

The stem: drop¬ --> normal; its equivalent statement is: normal¬ --> drop

A drop in gas mileage occurs only if a car's wheels are out of alignment: drop --> normal¬. Well, you can see that it confuses the necessary condition with the sufficient condition.

Misaligned wheels can sometimes cause a car's mileage to drop. If we negative this statement, then we have the statement: (normal¬ -- drop)¬. You can see this statement is in conflict with the statement implied in the stem. So it is the key.

cbb2

Beacuse my gas mileage has been steady during the same time period, ---------A

CONCLUSION: the alignment of my car's wheels must be normal.----B

GAP: A---B   

 NOT B-----NOT A is also correct

问ASSMUPTION,
其中一个选项是：

A drop in gas mileage occurs only if a car's wheels are out of alignment.

This one is not A---NOT B. MISTAKEN NEGATION

另外一个是：

Misaligned wheels can sometimes cause a car's mileage to drop.

This one is      NOT B----NOT A, CONTRAPOSITIVE.