GWD数学跪求大牛指导。。。急。。。。

xiaoyao750

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: A。。。。

13:

If the sequence x₁, x_2, x_{3, …,} x_n, … is such that x₁  = 3 and x_n+1
                                = 2x_n – 1 for n ≥ 1, then x₂₀ – x₁₉ =

 

A.     2¹⁹

B.     2²⁰

C.     2²¹

D.    2²⁰ - 1

E.     2²¹ - 1

Answer: A

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切尔西

Q20: 1）因为有40个人既不Favor M 也不Favor N， 所以推出不favor M 或者 N的总人数是42+20+35+35-40=90， 进而可以得出同时favor这两个的是10人

2）不知道有多少是not sure的，所以不充分

13： 
            x₁  = 3=2+1=2^1+1=>x_{n 等于2^n+1}

_所以： x₂₀ – x₁₉ =2^20-2^19=2^19