Multiplying by Multiples of 10

When we begin discussing multiplying by multiples of 10, we start by finding the factors of 100, 200, and 300. This is a great discussion, especially when we get to the factors of 200 and 300. The kids self-discover the relationship between the factors of 100 and the factors of 200 and 300. As we have this discussion, I casually comment that 4 x 50 and 50 x 4 both equal 200. I make this comment again when we get to 5 x 60 and 6 x 50 for 300. This leads the kids to notice the rule for multiplying by multiples of 10. We can just multiply the numbers that are NOT zero first, then we can add the appropriate amount of zeros. The kids absolutely think this is magic! :) Surely it isn't supposed to be this easy?!?!