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找到一题可以用这个方法解答的题目!
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 3.
题干可得:n=3a+2; t=5b+3
(1)n-2=3a 3a是5的倍数,那么说明a一定是5的倍数。3a是15的倍数,3a+2 mod 15=2
(2)t是3的倍数,说明5b是3的倍数,那么5b也是15的倍数。5b+3 mod 15=3
(1)+(2): nt mod 15= ((n mod 15)*(t mod 15))mod15=2*3 mod 15=6
选C
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