Video Transcript
Adding Numbers up to 20 on a Number Line
In this video, we’re going to learn how to add within 20 by jumping forward in ones
on a number line.
Now we know one way to find the answer when we’re adding two numbers together is to
start with the first number and then count on to find the answer. Well, in this video, we’re going to be practicing this skill of counting on. And we’re going to be using a number line to help us.
Just like its name suggests, a number line is a line labeled with numbers. And the numbers on the number line that we’re going to be using are going to start at
one and go all the way up to 20, because we’re going to be working within 20.
Now let’s say we’ve been asked to find the total of nine and five. Nine plus five equals what? Well, nine plus another five is the same as if we started at the number nine and then
counted on five more. So the first thing we can do is to take our first number and to find it on the number
line. Here it is. It’s the number just before 10, isn’t it? So this is where we’re going to start counting on from.
We need to find five more than nine. So we need to count on five ones. Let’s do that using the number line and see where we end up: one, two, three, four,
five. We started at the number nine, and we’ve ended on the number 14: nine, 10, 11, 12,
13, 14. We’ve used our number line to count on. We started at nine, counted on five, and we reached the number 14. So we can say nine plus five equals 14.
Now let’s put into practice what we’ve learned. We’ll try answering some questions where we have to count on using number lines.
Count on to add. Find the total. Eight plus seven equals what.
In this question, we need to find the total of eight and seven. And to help us, we can see that a number line has been drawn for us. In fact, this number line shows us how to work out the answer. We can find the answer by starting with the number eight and counting on another
seven. If we’re adding on seven, this is the same as adding seven ones or counting on one
seven times.
So let’s count on seven and see where we end up: one, two, three, four, five, six,
seven. And if we look underneath the number line, we can see that counting on seven is the
same as adding one seven times. We started with eight. And then we jumped to nine, 10, 11, 12, 13, 14, 15. The total of eight and seven is 15. And we found the answer by starting on the number eight and counting on seven. Eight plus seven equals 15.
Count on to add. Amelia started this calculation on a number line. Finish the calculation to find the total. 11 plus six equals what.
The calculation that we need to find the answer to in this problem is an
addition. We’re asked, 11 plus six equals what? And the very first sentence in this problem tells us how we’re to find the
answer. We have to count on to add. In other words, we need to start with the first number and count on from it.
Now if we look underneath the calculation, we can see a number line and we’re told
that Amelia started to work out the answer on a number line. We need to finish it to find a total. We can see that Amelia starts counting from the number 11. This is because the number 11 is the first number in the addition. Now she needs to add six. And this is the same as adding one six times. And we can see that she’s already added one three times.
Let’s put a counter on the number 11 and move it along our number line as we count on
six times. One, two three, this is as far as Amelia’s got up to, so let’s carry on counting up
to six, four, five, six. If we start at the number 11 and count on six, we get to 12, 13, 14, 15, 16, 17. 11 plus six equals 17. And we found the answer by starting with the number 11 on a number line and counting
on six more. The answer is 17.
Count on to add. Find the total. 12 plus six equals what.
In this problem, we’re told that we need to find the total. And the two numbers that we need to find the total of are 12 and six. We know this because we’re given a calculation: 12 plus six equals what. We know that one way we can find the total of two numbers is to count on. And we’re told to do this in the first sentence; count on to add.
We can use a number line to help us count on. We’re going to start with the number 12, which is the first number in our
addition. And we need to count on six more than 12. This is the same as adding one six times. So let’s count on six more than 12. And what we’ll do is we’ll mark the number line to show where we get to each
time. One, this takes us to 13. Two, we’re now at 14. Three, we know that 12 add three is 15; four, which takes us to 16. Five, 12 add five is 17. Six, six more than 12 is 18.
We found the answer by starting with the first number and then counting on to add the
second number. 12 plus six equals 18.
Now let’s go over what we’ve learned in this video. We’ve learned a way to add within 20 by jumping forward in ones on a number line.
