Prep 09 Math Q26

Wdrrrrrrr

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?

clz123134

尽量提3的倍数出来
7n+4 mod 3
=(6n+3)+(n+1) mod 3
=(n+1) mod 3
A

Wdrrrrrrr

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

感谢?