GWD两道，求助：）谢谢~~

lilyblue_zl

Q6:

The function f is defined for each positive three-digit integer n by f(n) = 2^x 3^y 5^z, where x, y and z are the hundreds, tens, and units digits of n, respectively.  If m and v are three-digit positive integers such that f(m) = 9 f(v), then m - v =

答案是20哈

Q36:

If x and y are integers, is y an even integer?

(1)     2y – x = x² – y²

(2)     x is an odd 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: A

帮忙看看上面两道题，脑子转不过来了，谢谢哈

wumeier

第二题的A得出y 不会等于even是吧？so A

ououbodao

第二题里面的整理以后的那个式子，右面是两个相邻的数字相乘，左面是间隔的两个数相乘..

lilyblue_zl

第二题选A哈

谢谢LS，不过我还有点疑问哈

第一题从这儿开始就没整明白了，能否麻烦帮忙祥解一下，谢谢

m=100x+10y+z,  n=100a+10b+c

一减搞定

另外， y(2+y)=x(x+1)，我纠结之处在于怎么都没找到一个数据来证明这个等式，或许只有X=0，Y=0的时候（也是偶数）？

bah-toronto

1.

f(m)=2^x 3^y 5^z 

f(v)=2^a  3^b5^c

f(m)=2^x 3^y 5^z =9f(v)=2^a  3^b+25^c

x=a, y=b+2, z=c

m=100x+10y+z,  n=100a+10b+c

一减搞定

2.把1式化成  y(2+y)=x(x+1)

右边必为even或0

左边必为odd或0

所以~~~~

xp635

Q6:

82^x3^y5^z

 

Q36

(1)  y(y+2)=x(x+1)

right hand: even

so, the left hand should be even, that is to say, y is even