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.
