Video Transcript
Word Problems: Addition and
Subtraction with Numbers up to 1,000
In this video, we will learn how to
decide which operations are needed to solve a word problem, by drawing a model if
necessary, and how to write an equation to record the solution. In this video, we’re going to learn
how to solve addition and subtraction word problems.
The first thing we have to do when
we’re trying to solve word problems is read the problem. Next, we have to choose the
operation: addition or subtraction. Once we’ve selected the operation,
we can use a model to help us think about how to calculate the answer.
If a doctor has 128 patients to see
in one week and he’s already seen 25 of them, this bar represents the number of
patients he still has left to see. This is a subtraction problem. We need to subtract the number of
patients the doctor’s already seen from the total number of patients he needs to see
this week to tell us how many patients he has left. Let’s subtract. Eight take away five is three. Two 10s take away two 10s leaves us
with no tens. And there’s nothing to subtract
from our 100. The doctor has 103 patients left to
see.
So when we’re trying to solve word
problems, first we need to read the problem and then use a bar model to help us
think about which operation to use. And then we calculate the
answer. Let’s put into practice what we’ve
learned now by trying some word problems.
A shop sold 790 books on Wednesday
and 205 books on Thursday. How many books were sold in those
two days?
In this question, we have to find
out how many books were sold on Wednesday and Thursday. We know the shop sold 790 books on
Wednesday and 205 books on Thursday. When we’re trying to solve word
problems, it helps to use a bar model. It helps us to see that to find the
total number of books sold on the two days, we need to add together 790 and 205. This is an addition problem.
There are lots of ways we could
find the answer. Let’s use the standard written
method. Zero ones plus five ones gives us a
total of five ones. Nine 10s plus no tens gives us a
total of nine 10s. And seven 100s plus two 100s gives
us a total of nine 100s. If a shop sold 790 books on
Wednesday and 205 books on Thursday, the total number of books they sold in those
two days is 995.
A farmer has 377 hens and 293
ducks. How many birds does he have
altogether?
This is a word problem. Usually, when we see the word
“altogether,” this means we need to add. So we’re being asked to find the
total number of birds. We know the farmer has 377 hens,
and we also know he has 293 ducks. When sketching a bar model in this
way, we can see what we need to do next. To find the total number of birds,
we need to add together 377 and 293. We could add using the standard
written method.
Let’s start by adding the ones. Seven ones and three ones gives us
a total of 10 ones. We can write our zero in the ones
place, and we need to carry the 10 into the tens column. Seven 10s plus nine 10s gives us 16
10s, plus the one we carried gives us 17. We can write the seven in the tens
column and the one in the hundreds column.
Now we just need to add the
hundreds. Three plus two plus one gives us a
total of six 100s. 377 plus 293 is 670. If a farmer has 377 hens and 293
ducks, then he has 670 birds altogether.
A shop has 953 bottles of
drink. 230 were sold. How many are left?
This is a word problem. We know the shop has 953 bottles of
drink. And we also know that 230 bottles
were sold. We have to calculate how many
bottles are left. Let’s sketch a bar model to
help. So we know the shop had 953 bottles
to begin with, and we know that 230 of them were sold. To calculate how many bottles are
left, we need to subtract 230 from 953.
Let’s use the standard written
method, 953 subtract 230. Let’s subtract. Three take away zero leaves us with
three ones. Five 10s take away three 10s leaves
us with two 10s. And nine 100s take away two 100s
leaves us with seven 100s. 953 subtract 230 equals 723. If a shop has 953 bottles of drink
and sells 230 bottles, they will have 723 bottles left. We solved this subtraction word
problem using a bar model and the standard written method. 953 subtract 230 is 723.
Olivia collected 796 stamps. If she gave 135 to her friend, how
many stamps are left?
This is a word problem. We’re being asked to calculate how
many stamps are left. It sounds like this is a
subtraction problem. We know that Olivia has 796 stamps,
and she gave 135 to her friend. So Olivia had 796 stamps. She gave 135 to her friend. And we have to calculate how many
stamps she has left.
To do this, we need to subtract the
135 stamps Olivia gave to her friend from the 796 stamps she had collected. We need to work out 796 subtract
135. Six ones take away five ones leaves
us with one. Nine 10s take away three 10s leaves
us with six 10s. And seven 100s take away one 100
leaves us with six 100s. If Olivia has 796 stamps and she
gives 135 to her friend, then she has 661 stamps left.
What have we learned in this
video? We have learned how to decide which
operations are needed to solve a word problem by drawing bar models. And we learned how to use these
models to help us write an equation.
