请教TTMath9中的两题

marco_polo

Q20:

 

	Favorable	Unfavorable	Not Sure
Candidate M	40	20	40
Candidate N	30	35	35

 

The table above shows the results of a survey of 100 voters each responded “favorable” or “unfavorable” or “not sure” when asked about their impressions of candidate M and of candidate N.  What was the number of voters who responded “favorable” for both candidates?

(1)   The number of voters who did not respond “favorable” for either candidate was 40.

(2)     The number of voters who responded “unfavorable” for both candidates was 10.

                  

A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.

B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.

C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.

D. EACH statement ALONE is sufficient.

E. Statements (1) and (2) TOGETHER are NOT sufficient.

Answer:

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答案A

Q26:

In the decimal representation of x, where 0 < x < 1, is the tenths digit if x nonzero?

(1)     16x is an integer.

(2)     8x is an integer.

                  

A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.

B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.

C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.

D. EACH statement ALONE is sufficient.

E. Statements (1) and (2) TOGETHER are NOT sufficient.

Answer:

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答案B

请教上述两题解决方法

笨笨和迷糊

这两道题我也不会，请高人指点！

scorpio7

第一题   对M N 均不偏爱的有四十个，即无论是单独偏爱M，单独偏爱N，抑或是两个都偏爱的总人数应该为100-40=60   表中favorable下的数据重复计数了，用40+30-60=10得出重复部分，即favorable for both    A正确   B得不出favorable和not sure之间的关系，错

第二题   既然16x是正数，且0<x<1,那么x= 1/16 ,2/16, 3/16  ...... 1/16最小，0.0625  后面的数tenth位均大于零    B选项同理，最小1/8，tenth位最小为1  ，可判断答案B

dianecarton

第一题确实有难度，我做的时候是列了9种情况一一比较。后来总结了一下这类题，因为是DS，所以要看清问的是什么，不要上来就大范围的列举或求值。

问的是既喜欢M又喜欢N的人数，而表格里我们已经知道了喜欢M的人数为40，喜欢N的人数为30，40+30=70=M+N+2MN 求MN。清楚了这个然后看条件（1），其实就是告诉了我们M+N+MN=100-40=60，于是能求出MN=10，所以条件1独立充分

再看（2）只能得到不喜欢MN的人数，然后得到或喜欢或不确定的人数，无法求喜欢MN的人数。不充分

提供的信息特别多的时候，不是每个数字都能用到的，筛选有用的信息是关键。

希望对楼主有所启发。

笨笨和迷糊

明白了,谢谢大虾们指教!