Re: [計量] The reflection of a postive integer ...

看板GRE作者collegeman (通體舒暢)時間15年前 (2008/10/21 10:39)推噓2(2推 0噓 2→)

留言4則, 3人參與討論串2/2 (看更多)

※ 引述《Fnymph (~(=o=)~)》之銘言： : The reflection of a postive integer is obtained by reversing its digits. : For example, 321 is the reflection of 123. The difference between a : five-digit-integer and its reflection must be divisive : by which of the following? : a 3 : b 4 : c 5 : d 7 : e 9 : A: e : 請問各位，這題該怎麼算阿... 假設原五位數為 ABCDE，則 ABCDE = 10000 * A + 1000 * B + 100 * C + 10 * D + 1 * E 其 reflection 為 EDCBA 為 EDCBA = 10000 * E + 1000 * D + 100 * C + 10 * B + 1 * A 兩者相減後為 ABCDE - EDCBA = 9999 * A + 990 * B + 0 * C - 990 * D - 9999 * E = 9 * (1111 * A + 110 * B - 110 * D - 1111 * E) 所以可以被 9 整除，選 E。 -- ※ 發信站: 批踢踢實業坊(ptt.cc) ◆ From: 140.109.19.239

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Scwen

10/21 10:42, , 1^F

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collegeman

10/21 10:47, , 2^F

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collegeman

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