GWD 26-11

gchen030

Q11:

How many different factors does the integer n have?

(1)   n = a⁴b³, where a and b are different positive prime numbers.

(2)             The only positive prime numbers that are factors of n are 5 and 7.

                  

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.

Why A?  I think B is sufficeint too, pls tell me it isnt?

Q13:

If x is negative, is x < -3?

(1)   x² > 9

(2)             x³ < -9

                  

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.

Why A?  I think B is sufficeint too, pls tell me it isnt?

Q18:

If 9x = 27^y, which of the following expresses x in terms of y?

 

A.          3^y

B.          3^y-1

C.          3^2y-1

D.          3^2y-3

E.          3^3y-2

Thanks in advance!

[此贴子已经被作者于2009-2-5 10:57:15编辑过]

wentaow2008

   第一题的（2）条件比较麻烦啊～小弟只有慢慢套数字来试的方法来了（1）条件是可以的。第二题（2）不可以啊，是-2.5满足，而3.5也可以满足，没法判断！第三题easy，9就是3的二次方，27的y次方就是3的3y次方啊～所以E.

suconnan

第一题：（2）说是有5和7，但是不知道有几个，一个5和一个7，那就只有4个factors（1，5，7，35）,10个5和10个7，那就有（10+1）*（10+1）=121个factors。

gchen030

谢谢啦， 第3题是挺简单的。  我没看清楚。 太粗心了