Look at how Natalie broke apart a number to help her add, 138 plus 40. First, add the tens. 30 plus 40 equals what. Then add to find the total.
In this problem, Natalie is adding a three-digit number and a two-digit multiple of 10 together. Her three-digit number is 138. And the multiple of 10 that she’s adding to this is 40 or four tens. Now, the number that Natalie begins with, 138, is made up of one hundred, three tens, and eight ones. And the number that she’s adding, 40, has a value of four tens. Now, because Natalie is adding a number of tens to this three-digit number, she breaks apart the number to separate out the tens that she needs to add together. In other words, she takes the three tens from the number and she moves them to one side. And we can see this in the way that she separated out her base 10 equipment. 138 has been split into one hundred and eight ones, that’s worth 108, and then three tens; that’s worth 30.
Now, we can continue using her method to find the answer. In the first step, we’re told to add the tens together. 30 plus 40 equals what. Well, we know that three plus four equals seven. And so three tens plus four tens equals seven tens or 70. And we can show this by adding the two sets of blocks together. Now although we’ve added the tens, our number is still broken apart. On one side, we have 108 and on the other side, we have our total of our tens, which is 70. That’s why in the second part of our problem, we’re asked to add them together to find the total. What is 108 plus 70? Well, if we add 108 and 70 together, we get an answer that’s made up of one hundred, seven tens, and eight ones. The answer is 178.
To find the total of 138 and 40, we first realised that we were adding a number of tens. And so we looked at how Natalie had broken apart the number 138 to separate out the tens. This helped us to add them. 30 plus 40 equals 70. Once we added the tens, we could then combine this back with the other part to find the total. 108 plus 70 is the same as the answer to the calculation, which was 138 plus 40. And the answer is 178. Our two answers are 70 and 178.