og 13 ds 80, 133 （两道新题答案解析讨lun)

lostkiki

DS 80: If R ans 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. Answer:  A
对选项1的解释如下：it is given that s is a factor of 100 and so s = 1, 2, 4, 5, 10, 20,25, 50, 100. this means that r/s musbt be one of the quotients r/1, r/2,r/4,...r/100. Thus , r/s must be one of th products r(1), r(0.5), r(o.25), r (0.2), or r (0.01). 以上都不难理解，注意，问题来了： -in each case, r/s is the product of an integer and a decimal with a finite number of nonzero digits, and hence, r/s can be expressed as a decimal with a finite number of nonzero digits, In fact, it suffices to not this is true for r/100, since eatch of other possibilities is a positive integer times r/100.
楼主疏于学习数学数年，现在搞不清对有限小数的定义是否也包括整数。 因为当s=1, r/s 是整数integer啊，而非 "a decemal with only a finite number of nonzero digits".
求解！！
DS 133: If x, y, z are three digit positive intgers and if x=y+z, is the hundreds digit of x equal to the sum of th hundreds digits of y and z?
(1) the tens digits of x is equal to the sum of the tens digits of y and z; (2) the units digit of x is equal to the sum of the units digits of y and z. Anwer : A
答案解析完全看不懂， 有没有高手能给出更简介明了和严谨的思路？

谢谢！！！

JuliaLiu1026

我也再问80题。。。。我连题都没大读懂，问的是：分数r/s可以被表示成为一个仅有有限个数字组成的非零数字的小数吗？求解啊 。。。。。

lifeforest

lostkiki, 看这里：http://www.kaogmat.com/wiki/Expl ... b01d04b93b420010100

总结下， 整数就是 n.0000000, 是有限的nonzero digits + zeros, can be expressed as decimal with only a finite number of nonzero digits.

lifeforest

回帖怎么还要评审？？

lifeforest

嗯，看来是因为有外部链接。链接里面的内容就是 整数 是 n.0000000000... can be expressed as decimal with a finite number of nonzero digits