Multi-Digit Multiplication Strategy: Break Apart Factor(s) Using Landmark Numbers

Today we reviewed how to take a factor and

A landmark number is a familiar number (we know right away where it is--what comes before and after it on the number line) used to help count more efficiently.  Many landmark numbers are multiples of 5 or 10.  We can use landmark numbers when breaking apart factor(s):

Over the past two weeks, students have explored what happens when multiplying by a multiple of ten, how it is similar to multiplying by one.  We've done many think-alouds that sound something like this:

Since 3x15 is 45, we can use 45 as our "leading numbers", but we need to remember that we're multiplying with a multiple of ten (150), so it's really like 45 tens, which has a value of 450.
 
(Yes, you can also just cover up any zeros, multiply, then put the zero(s) on the end, but conversations like this will give students a much greater understanding of why they are doing what they're doing, increasing their number sense.)

 
If 3x15 is still intimidating, we've also talked about how you can think about it as 3x10 and 3x5, then combine the products.