标题: 请教一道gmatprep难题。 [打印本页]
作者: 小腾 时间: 2006-4-20 07:21 标题: 请教一道gmatprep难题。
when positive integer n is devided by 3, the remainder is 2, when positive interger t is divided by 5, the remainder is 3, what is the remainder of nt when devided by 15?
(1) n-2 is divided by 5
(2) t is divided by 3
谢谢各位NN指教！
作者: meimei5656 时间: 2006-4-20 19:21
1. When positive integer n is divided by 3, the remainder is 2; and when positive integer t is divided by 5, the remainder is 3. what is the remainder when the product nt is divided by 15?
1) n-2 is divisible by 5 2) t is divisible by 5
Answer: C
第2个条件抄错了吧？
n=3k+2,t=5s+3
nt=15ks+9k+10s+6
这就是解答。 以上式子是从题目推出. 好像也没说到底怎么做.
整除的题老是做不对, 还请牛人支招啊.
作者: renprince 时间: 2006-4-22 07:45
1. When positive integer n is divided by 3, the remainder is 2; and when positive integer t is divided by 5, the remainder is 3. what is the remainder when the product nt is divided by 15?
1) n-2 is divisible by 5 2) t is divisible by 5
Answer: C
第2个条件抄错了吧？
n=3k+2,t=5s+3
nt=15ks+9k+10s+6
这就是解答。 以上式子是从题目推出. 好像也没说到底怎么做.
整除的题老是做不对, 还请牛人支招啊.
对,154题条件（2）写错了，本贴才是对的，t能被3整除。
根据题干n=3k+2
条件（1）n-2=5m，n=5m+2,与题干联合可得通项n=15p+2
根据题干t=5s+3
条件（2）t=3l,与题干联合可得通项t=15q+3
nt=(15p+2)(15q+3)=(15^2)pq+45p+30q+6
除以15余6
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