WEBVTT
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Addition or Subtraction Word Problems within 100
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In this video, we will learn how to model addition or subtraction word problems using bar models.
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We can use bar models to help us visualise word problems in our heads.
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For example, this bar model shows 100 tickets available for a school play.
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25 are sold.
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How many tickets are left?
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So, this bar represents the 100 tickets.
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If 25 tickets are sold, we need to work out how many are left.
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There would be 75 tickets left.
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In this example, the bar model was used to calculate 100 take away 25 equals 75.
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Letâ€™s practice solving some word problems using bar models.
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David and Jennifer were building houses out of blocks.
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David used 36 blocks.
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Jennifer used 51 blocks.
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How many blocks did they use?
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Will the answer be bigger or smaller than the numbers in the question?
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Do you need to add or subtract to find the answer?
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Find out how many blocks they used.
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The question tells us David used 36 blocks and Jennifer used 51.
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This bar model shows the 36 blocks that David used and the 51 blocks that Jennifer used.
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The blue bar shows the total number of bricks used.
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So, we can see that the answer will be bigger than the numbers in the question.
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We need to add 36 and 51 to give us the answer.
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If we partition 36 and 51, that will make it easier for us to add these two numbers together.
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36 is 30 and six.
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51 is 50 and one.
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One and six makes seven.
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50 and 30 makes 80.
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80 and seven is 87.
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So, Jennifer and David used 87 blocks altogether.
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We used a bar model to help us picture what the problem looked like.
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Then, we could work out the answer.
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The answer will be bigger than the numbers in the question.
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We had to add to find the answer.
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And the total number of blocks used was 87.
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Emma is trying to solve this word problem.
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There were 41 birds in a tree.
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15 of them flew away.
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How many birds are in the tree now?
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Emma said the answer was 41 plus 15 equals 56.
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What did she do wrong?
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What is the correct answer?
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We can use a bar model to help us picture the problem.
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We know there were 41 birds in the tree.
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15 of them flew away.
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We need to work out how many birds are left.
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To find out how many birds are left, we start with 41 and we need to subtract 15.
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We could partition 15 into a 10 and a five.
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First, we can take away 10 from 41, which is 31.
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Then, we can take away five from 31, 30, 29, 28, 27, 26.
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So, 41 take away 15 is 26.
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What did Emma do wrong?
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What is the correct answer?
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Emma added to find her answer.
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She calculated 41 plus 15 equals 56.
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So, she added when she should have subtracted.
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The answer is 41 take away 15 equals 26.
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We used our bar model to help us picture the problem.
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We had 41 birds.
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15 flew away.
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There are 26 birds in the tree now.
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To find the answer, we subtracted.