Is 1003 a multiple of three?

No, all multiples of three can be worked out easily. The sum of all the numbers must add up to 3, 6 or 9. For example, 1+0+0+3 = 4 so it is not a multiple of 3. Another example is 876. 8+7+6=21 2+1=3 so 876 is a multiple of 3.