A New Way to Add Two and Three Digit Numbers

March 11, 2016 

We have been working on different strategies for adding two digit numbers. We already know that we can add tens and ones, use an open number line, or make friendly numbers. Over the last few days we have learned a new strategy called the Partial Sums Algorithm. It is really fun once you get the hang of it, but it might look a little different than the way our Moms and Dads learned to add.

Here's what we did!

We are adding using concrete models based on place value.

 These Base 10 blocks represent the expanded form of each number.

We combine our longs and cubes and record each sum separately.

Then we find the total sum. 

Now we are starting our new problem by writing a "ballpark estimate." It will help us know if our answer is reasonable.

 We are modeling our numbers by drawing longs and cubes.

 We record the sum for the tens.

We record the sum for the ones.

We find the total.

Easy Peasy!

Remember to compare your answer to your Ballpark Estimate!

Is it close?

Here are the steps to the Partial Sums Algorithm.

 Write a Ballpark estimate.

 Model in longs and cubes. (You will be able to skip this step once you know the steps).

 Add the tens.

 Record the sum.

Add the ones.

 Record the one's sum.

Add the two sums for the total.