when the positive integer n is divided by 7, the remainder is 2. what is the remainder when 5n is decided by 7
let n = 37
37/7 = 5 + 2/7
then 5n = 185
185/7 = 26 + 3/7
n/7 = k + 2/7
5n/7 = 5k + 10/7 , don't care about the 5k, just the remainder part
but 10/7 = 1 + 3/7
so the remainder is 3, as illustrated in my example