two preps need help!!!

scottrade

12.1013-!-item-!-187;#058&000609

Of the 25 cars sold at a certain dealership yesterday, some had automatic transmission and some had antilock brakes.How many of the cars had automatic transmission but not antilock brakes?



(1)All of the cars that had antilock brakes also had automatic transmission.



(2)2 of the cars had neither automatic transmission nor antilock brakes.

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【答案】E

???why not C

scottrade

23.    1653-!-item-!-187;#058&000843
At least 100 students at a certain high school study Japanese. If 4 percent of the students at the school who study French also study Japanese, do more students at the school study French than Japanese?

(1)  16 students at the school study both French and Japanese.

(2)    10 percent of the students at the school who study Japanese also study French.
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【答案】B


Why not A but B?
Confused!

yzg1236

lz，最好讲汉语

tkrayla

1) 有AB的也有AT 所以有AB的是有AT的子集
i.e. AB<AT  not sufficient
2) 有2辆既无AB也无AT 还是得不到答案
1+2 有AB或AT的有23(25-2) AB<AT 有AT无AB=23-AB
但是 不知道AB有多少
so E

tkrayla

这道题有个隐含条件 就是不管是学J&F占J或F的比例是多少 学J&F的人数总是固定的
1) J&F16人 F=16/0.04=400
但是 J>100 无法比较F和J的大小
2) 设J&F为X
F=X/0.04 J=X/0.1 显然 F>J的
所以 B

scottrade

明白了，非常感谢