Video: Addition or Subtraction Word Problems Within 100

In this video, we will learn how to model addition situations up to 100 with bar models or part-part-whole diagrams.

05:19

Video Transcript

Addition or Subtraction Word Problems within 100

In this video, we will learn how to model addition or subtraction word problems using bar models. We can use bar models to help us visualise word problems in our heads.

For example, this bar model shows 100 tickets available for a school play. 25 are sold. How many tickets are left?

So, this bar represents the 100 tickets. If 25 tickets are sold, we need to work out how many are left. There would be 75 tickets left. In this example, the bar model was used to calculate 100 take away 25 equals 75.

Let’s practice solving some word problems using bar models.

David and Jennifer were building houses out of blocks. David used 36 blocks. Jennifer used 51 blocks. How many blocks did they use? Will the answer be bigger or smaller than the numbers in the question? Do you need to add or subtract to find the answer? Find out how many blocks they used.

The question tells us David used 36 blocks and Jennifer used 51. This bar model shows the 36 blocks that David used and the 51 blocks that Jennifer used. The blue bar shows the total number of bricks used. So, we can see that the answer will be bigger than the numbers in the question. We need to add 36 and 51 to give us the answer.

If we partition 36 and 51, that will make it easier for us to add these two numbers together. 36 is 30 and six. 51 is 50 and one. One and six makes seven. 50 and 30 makes 80. 80 and seven is 87. So, Jennifer and David used 87 blocks altogether. We used a bar model to help us picture what the problem looked like. Then, we could work out the answer. The answer will be bigger than the numbers in the question. We had to add to find the answer. And the total number of blocks used was 87.

Emma is trying to solve this word problem. There were 41 birds in a tree. 15 of them flew away. How many birds are in the tree now? Emma said the answer was 41 plus 15 equals 56. What did she do wrong? What is the correct answer?

We can use a bar model to help us picture the problem. We know there were 41 birds in the tree. 15 of them flew away. We need to work out how many birds are left. To find out how many birds are left, we start with 41 and we need to subtract 15. We could partition 15 into a 10 and a five. First, we can take away 10 from 41, which is 31. Then, we can take away five from 31, 30, 29, 28, 27, 26. So, 41 take away 15 is 26.

What did Emma do wrong? What is the correct answer? Emma added to find her answer. She calculated 41 plus 15 equals 56. So, she added when she should have subtracted. The answer is 41 take away 15 equals 26. We used our bar model to help us picture the problem. We had 41 birds. 15 flew away. There are 26 birds in the tree now. To find the answer, we subtracted.

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