Description: Sal uses strategies, such as an understanding of place value, to multiply numbers like 800x400. Now let's work this through together, and I'm going to work it out in a way that at least my head likes to tackle it. Once you get enough practice, you might even be able to do these types of multiplication problems without even needing to use paper. And if you're multiplying a bunch of numbers like this, you can switch the order in which you're doing the multiplication.*Teacher Advisor is 100% free.