Video Transcript
Missing Numbers in Addition
Equations
In this video, we’re going to learn
how to find the missing addend in an addition equation using numbers up to 10. Let’s start by thinking about a
trick that you could do with your friends. Here’s a line of marbles. If we count them, we can see that
there’s a total of five. If we were drawing a part–whole
model, we could say that the whole amount is five. Now, let’s imagine that we have a
plastic bowl and we say to one of our friends to turn it upside down and to cover up
some of the marbles. There we are. Our friend has covered a part of
the whole amount using the bowl.
But how many marbles are underneath
the bowl? How can we give the answer without
looking? Well, we can use what we know about
addition equation and parts and wholes to help us. As we’ve said already, we know that
the whole number of marbles was five. And we can see part of this whole
amount. There are three marbles that aren’t
covered up by the bowl. We need to use what we know to find
the missing part. These are the marbles that have
been covered up by the bowl. We could even write this problem as
a number sentence. What plus three makes five. Five is made up of three and
another number. What is that other number? We can count on to find the missing
part.
Let’s use part of a number track to
help us. Remember, we’re trying to find
which number goes with three to make five. We could start by putting a counter
on the number three and then seeing how many times we need to move our counter to
get to five, one, two. We know that two goes with three to
make five. So we can say our missing part in
our part–whole diagram is the number two. And we can complete the missing
number in our addition equation. Two plus three equals five. And that’s how we can turn to our
friend without looking underneath the bowl and say, “I know that you’ve hidden two
marbles underneath the bowl.” Shall we check? Here they are. Two is a part. Three is a part. The whole is five. Now let’s have a go at using what
we know about addition equations to help find some missing numbers.
Find the missing number. One plus what equals four.
We can see two missing spaces
here. To begin with, we’re given an
addition equation. And instead of the missing number
being at the end like it often is, we can see that one of the numbers we’re adding
is missing. One plus what equals four. And underneath this equation, we
can see the same addition shown using pictures. One ball plus how many balls equals
four balls. The number that’s missing in this
question is one of the parts. To help us understand this, we
could sketch a part–whole model. Now we know the whole amount
because the answer to the addition or the total is four. This whole amount is what happens
when we add two parts together.
What else do we know? Well, we also know that one of the
parts is worth one. So one is a part, another number is
a part, and the whole amount is four. How can we find the missing
part? Well, we could count on from the
part we already know. Let’s use cubes to help us do
this. This cube represents the part that
we already know, which is worth one. Now let’s count on until we get to
four cubes, two, three, four. We’ve counted on three more cubes
to make a chain of four cubes. So we can complete our part–whole
model using the number three. One and three go together to make
four. Four is equal to one and three. Our missing number is three.
There are six rabbits and four of
them do not have carrots. How many rabbits have carrots? What plus four equals six.
We can see that the missing number
in the equation that we’re given in this problem isn’t at the end. Often we do have to find the total
number if we’re adding two numbers together. But in this problem, we need to
find one of the parts that we add together. Our missing number is the first
number in the addition. What add four equals six. To help us find this missing
number, let’s look at what the problem’s describing. To begin with, we’re told that
there are six rabbits. Now, are these six rabbits part or
the whole amount? Well, if we count them quickly, we
can see that they are the whole amount, the total. There are six rabbits
altogether.
So if we were drawing a part–whole
model, we’d write the number six to represent the whole. And our whole line of six rabbits
is split into two parts. We’ve got a group of rabbits that
do have carrots and then another group of rabbits that do not have carrots. And we don’t need to count this
second group because we’re told in the question four of the rabbits do not have
carrots. So part of the whole amount is the
number four. And we’re asked how many rabbits
have carrots. In other words, what number goes
together with four to make a total of six?
We could use counters to model the
problem. We could use six counters to
represent our six rabbits. Now, four of our rabbits do not
have carrots. So perhaps we could use a
different-colored counter, one, two, three, four. So if these pink counters represent
the rabbits that do not have carrots, let’s count the white counters. These are the rabbits that do have
carrots. We can see that there are one, two
white counters. And of course, we could count the
rabbits in the picture, one, two. The number two goes with the number
four to make a total of six. Six is equal to two plus four. And so if there are six rabbits and
four of them do not have carrots, the number of rabbits that do have carrots is
two.
Fill in the blank. What plus three equals seven.
In this addition equation, we’ve
got a missing number. Now, often with an addition
equation, the missing number comes after the equal sign. We need to add together two numbers
to find out what that total or the whole amount is. But what’s different about the
addition equation that we have here? The missing number is one of the
numbers that we’re adding together. We know what they make because we
can see that the addition equals seven. The whole amount is seven. Our addition equation also shows us
one of the parts that makes up seven. And that’s the number three. Something add three equals
seven. And what is that something? What part goes together with three
to make seven?
We could count on to help us find
the answer. And to do that, we could use a
number track, so let’s do that. We could start by pointing to the
number three. Let’s see how many numbers we need
to count on to get to a total of seven, one, two, three, four. Three and four are two parts that
go together to make a total of seven. So we could complete our part–whole
model to show the number four. And we could also fill in the blank
in our addition equation. We can make seven out of three and
four. Four plus three equals seven. The missing number is four.
So what’ve we learned in this
video? We’ve learned how to find the
missing addend in an addition equation with numbers up to 10.
