Adding 2-Digit Numbers

Mr. Squeaks and Imani are taking part in the annual lake clean up contest. They are hoping this is the year they will take their place on the winners' stand! Although the real reward is a clean lake, the winner of this contest will be the participant that collects the greatest total weight of litter. In order to find the winner we need to use an efficient, or quick, way of adding sets of numbers called column addition. “Adding Two Digit Numbers Using Column Addition" Let’s look at the items our contestants have retrieved from the lake. As you can see we have several two digit addition problems to solve, so we will want to use the best way to find the answers without having to do a lot of steps. Let's use the spotted mouse's numbers as an example. Spotted Mouse collected a thirty-six kilogram bike and a twenty-two kilogram chair. You already have been shown how to add two digit numbers using number lines and the base ten blocks. In the column addition, we use those same ideas, but we simplify the problem. We set the equation up vertically, with one number or addend on top of the other in order of their place values. We line up the place values by putting the two underneath the six and the two tens under the three tens. Make sure to include the addition sign. We always want to remember what we are supposed to be doing with the numbers. We will find the sum of the numbers by adding the digits from right to left, beginning with the ones place. What is six plus two more? Place the eight below the line directly under the ones place. Next, we move one place over to the left and now we add the tens place. How many are three tens and two tens? We can write the digit five below the line under the tens place because the five represents five tens or fifty. Spotted Mouse collected fifty-eight kilograms of litter. Let’s try it out with Imani's finds and see how she did. We are going to find the sum of fourteen and forty-seven. Starting with the ones, four plus seven equals eleven. What do you notice about the sum of the ones place? Eleven is a two digit number made of one one and one ten. So one is written underneath the ones place and one is regrouped on top of the tens place. Now we add the tens, including this new value added at the top. What is the sum of ten, forty and ten? Sixty. So,we have six tens. Imani took sixty-one kilograms of litter from the lake. Wow! There is one more contestant that needs their collection rounds added. Our own, Mr. Squeaks! How did Mr. Squeaks do in the contest? We set up the problem by writing the sixty-five over the seventy-four. We add five and four in the ones place and get nine. No regrouping is needed. We add six and seven in the tens place and that made thirteen tens. Hmmm, we have more than one digit in this answer. Based on the last problem, can you think what we need to do next? When we have a two digit sum, we'll regroup it to the next place value. The next place value is the hundreds. Because thirteen has a value greater than ten, we regrouped the final digit, one, to the hundreds place. Mr. Squeaks has one hundred and thirty-nine kilograms! Remember in column addition, we line up numbers vertically, or one top of the other, based on place values. We start adding with the ones place and move to the left to add the tens. Sometimes we need to regroup into the next place value when our answer is greater than ten. Let’s head back to the leader board and see about declaring a winner! Yes! He did it! Mr. Squeaks has taken first place! Congratulations Mr. Squeaks, well done! You've won the trophy and everyone made the lake beautiful again!