求解 GWD-10-19、25、26

lindaaniu

Q26:
What is the greatest common factor of the positive integers j and k?
(1)      k = j + 1
(2)      jk is divisible by 5.
    
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
Q25:
If the sequence x1, x2, x3, …, xn, … is such that x1  = 3 and xn+1 = 2xn – 1 for n ≥ 1, then x20 – x19 =

A.    219
B.    220
C.    221
D.    220 - 1
E.    221 - 1
Answer: A
Q19:
In a certain region, the number of children who have been vaccinated against rubella is twice the number who have been vaccinated against mumps.  The number who have been vaccinated against both is twice the number who have been vaccinated only against mumps.  If 5,000 have been vaccinated against both, how many have been vaccinated only against rubella?

A.    2,500
B.    7,500
C.    10,000
D.    15,000
E.    17,500
Answer: C

如题，谢谢！！

lindaaniu

自己顶起来，求助！

lindaaniu

再顶！求解！

afei0128

Q26:
What is the greatest common factor of the positive integers j and k?
(1)      k = j + 1
(2)      jk is divisible by 5.

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

我试着解一下这个。

条件1：显然可以。根据条件可以得出j和k是相邻的两个正整数，于是最大的公约数必然是1.
条件2：举例，不能确定最大公约数。如j=2,k=5,此时最大公约数为1；如j=10,k=5,此时最大公约数为k

所以选A

请指教，谢谢