Explain how you know that 197 is not a multiple of 3

If a number is a multiple of another number, that means that when you divide the number by the other number, it shouldn't be a decimal. That being said, what happens when we do 197/3? You get a decimal, not a whole number. Therefore 197 is not a multiple of 3. Also, this totally isn't a high school question =P 

THE simple way of writing this is that when you add up the digits of any multiple of three,they sum too will be a multiple of three(try it yourself). However,when you do 1+9+7 you get 17,which is not a multiple of three(17/3=5.66666)