求教一道数学题

callmesoli

If r and s are positive integers, can the fraction r/s be expressed as a decimal with only a finite number of nonzero digits?

(1) s is a factor of 100

(2) r is a factor of 100

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 statement TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
D.EACH statement ALONE is sufficient.
E.Statements (1) and (2) TOGETHER are NOT sufficient.
我认为选E，答案选A， 我认为A的反例很多~比如r=5 s=100 r\s=0.05 即不符合题目所说finite number of nonzero digit .

sophialaw81

a decimal with only a finite number of nonzero digits

This is to exclude: 0.1000000...

callmesoli

好吧~我对这句话的理解是 有限个非零数位 重点是在非零上~即 0.05中有一个0是零数位。不符合~~

henryest

答案是A, 完全没有错误，r=5，s-100不是反例好么……finite number of

nonzero digits的意思是有限个非零数字，0.05只有一个非0数字5可不就是1

个非0数字么，1个还不是有限个那多少个是呢……做题仔细点就不会错啦