标题: Prep 09 Math Q26 [打印本页] 作者: Wdrrrrrrr 时间: 2019-10-2 16:32 标题: Prep 09 Math Q26 If n is a positive integer and r is the remainder 4+7n is divided by 3, what is the value of r?
(1)n+1 is divisible by 3
(2)n>20
求详细思路?作者: clz123134 时间: 2019-10-2 17:15
尽量提3的倍数出来
7n+4 mod 3
=(6n+3)+(n+1) mod 3
=(n+1) mod 3
A作者: Wdrrrrrrr 时间: 2019-10-3 11:46
clz123134 发表于 2019-10-2 17:15
尽量提3的倍数出来
7n+4 mod 3
=(6n+3)+(n+1) mod 3