We are continuing to work through this addition and subtraction unit. This week we will be focusing heavily on the specific strategies we can use to add 2 (and 3) digit numbers. Here are the strategies we will be using. We haven’t introduced them all this year yet but your child may remember them from grade 2. Please keep in mind, it’s not a requirement for children to master all the strategies. Some students will only be able to use 1-2 strategies successfully, while others are able to use all of them. The end goal is for each student to be able to add 2 and 3 digit numbers successfully, using a strategy that works for them.
The easiest way to start is by drawing a picture or using Base Ten blocks:
Drawing the picture (above) is basically the same as adding the ones last (below): You start by adding the hundreds together, then you add the tens together, then the ones together. The final step is adding all three numbers into one number.
Here is another way to add the ones last: This strategy is basically “counting on”, and is the best strategy to use for those students who may struggle with addition & subtraction.
Here is the Friendly Number strategy. It works best when one of your numbers is already almost a Tens number (ends in a zero):
This is the traditional algorithm (adding the ones first). We teach this strategy AFTER the others, and that is because we want students to have a SOLID understanding of place value before using this strategy. Often, students will master this strategy but CANNOT explain their strategy or what they are actually doing. One thing to remember when using this strategy is that each column is a different place value. In the first equation below, 214 + 373, the 1 + 7 column is not 1 +7, it is 10 + 70. Often students do not think of these numbers in their true place value amount, and that’s what leads to confusion when we start to regroup (like the second example).
Please let me know if you have any questions as we go through these strategies in class.