Video Transcript
Subtracting by Counting Back:
Numbers up to 10
In this video, we will learn how to
subtract within 10 by counting back from the starting number. We can use a number line to help us
count back or subtract.
Let’s practice counting back from
10. 10, nine, eight, seven, six, five,
four, three, two, one, zero. Let’s think about how we can use
counting back on a number line or a number track to help us subtract. How could we calculate 10 subtract
four using a number line? If the amount we start with is 10,
then we need to start at number 10 on the number line. We need to subtract four from
10. So, we need to start at number 10
and count back four on the number line. One, two, three, four.
We started at 10. We counted back four. And we finished counting at number
six. We subtracted four from 10 by
counting back four. Counting back is the same as
subtracting. Let’s practice what we’ve learned
with some questions.
To find seven take away four, we
can start at seven and count backward four. Seven, six, five, what, what. Finish counting backward to find
the answer to seven take away four.
In this question, we have to find
the answer to seven take away four. When we see the words “take away,”
we know that that means subtract. We would write this as seven
subtract four. The question also tells us to start
at number seven and count backward four. We can see that some of the numbers
have already been written. Seven, six, five. What comes next? If we start at seven and count
backward, seven, six, five, the next number is four. Seven, six, five, four, three.
We started at seven. We counted backward or subtracted
four. We finished counting at number
three. To find seven take away four, we
started at seven and counted backward four. Seven, six, five, four, three. The answer to seven take away four
is three.
There were nine balls in a box. Then, five of them were
removed. How many balls are left?
This is a word problem. Let’s look carefully at the
information we’re given. To start with, we’re told that
there are nine balls in a box. Then, five of them were
removed. If the balls were removed, that
means they were taken away. We have to work out how many balls
are left.
Have you worked out what kind of
problem this is? When we have a number of balls and
we take some away, we need to subtract. So, there were nine balls in a
box. And five were removed or taken
away. To find out how many balls are
left, we need to take away five from nine. Let’s use a number line to help us
subtract.
We need to start at number nine
because there were nine balls in the box at the start. We have to take away five. That means we need to count
backward five starting at number nine. One, two, three, four, five. Nine, eight, seven, six, five,
four. Nine take away five equals
four. To help us subtract, we started at
number nine on the number line and we counted back five. If there are nine balls in a box
and five of them are removed, there will be four balls left. Nine subtract five equals four.
Count back to find nine take away
four.
In this question, we have to use
the number line to help us count back to find the answer to nine take away four. We need to start at number nine and
count back four on the number line to find the answer. The jumps have already been drawn
for us. We just need to start at nine and
count back. Nine, eight, seven, six, five. Nine subtract four equals five. We used the number line to help us
count back to subtract. Nine, eight, seven, six, five. Nine take away four equals
five.
Write The subtraction equation. Is it six subtract one equals
three, six subtract three equals three, six subtract three equals two, or six
subtract four equals three?
In this question, we have to find
the subtraction equation which matches the number line. Let’s look more closely at what’s
happening on the number line. We started counting at number
six. So, we know the starting number or
the first number in our subtraction equation should be number six. But that doesn’t help us much
because all of these subtraction equations start with the number six.
How many times did we count back on
this number line from number six? There are three arrows, which must
mean that we have to subtract three. One, two, three. If we count back three, that’s the
same as subtracting three. Either of these two equations could
be correct because both of these are subtracting three. Is six subtract three three? Or is six subtract three two?
Let’s start at six and count back
three. Six, five, four, three. We finished counting at number
three. The subtraction equation which
matches the number line is six subtract three equals three. If we start at six on the number
line and count back three, we will finish counting on number three. Six subtract three equals
three.
What have we learned in this
video? We have learned how to subtract by
counting back on a number line.
