[求助]GWD 29-32 數學題DS

bigwish

Q32:

In the decimal representation of x, where 0 < x < 1, is the tenths digit of 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.

ANS:B

請教一下這題的思路,謝謝^_^

mikejia

16X是整数, 那么X可能是 0.0* 或0.1* , such as 0.5 or 0.05, and the tenths digit of 0.05 is 0,

then we consider the 8x, if 8x is integer, the x could be 0.125, 0.25 .., cannot be 0.0*, coz 0.0* times 8 cannot equal to one intger.so the tenths of x based on integer of 8x also is a nonzero.

so the answer is B

oldersea

我怎么觉得答案是D啊。

1）x的最后一位必为5,而0.05x16=0.8不为整数. so the tenths digit of x must be nonzero.

2）同上。

mikejia

the 16x is integer

the 8x is integer

are the premises of this question, how can you consider them as no-integers?

[此贴子已经被作者于2006-8-2 19:49:08编辑过]