Video Transcript
Ordering Two-Digit Numbers
In this video, we’re going to learn
how to order numbers up to 100. And we’re going to do this by
comparing the number of tens and ones.
In a moment, we’re gonna have a go
at putting some numbers in order. The word order really means sort
out. And we can sort out in one of two
ways. There’s ascending order, which
means we go from least to greatest. So, if we’re putting numbers in
ascending order, we start with the smallest and we go all the way up to the
biggest. The opposite of this is descending
order, where we go from greatest to least. When we order numbers like this, we
start with the biggest number and we go all the way through to the smallest. Now, to be able to put two-digit
numbers in order, all we have to do is be able to compare them. How good are you at comparing
numbers? Let’s have a go.
Here are three front doors. If we look carefully, we can see
the numbers of each house are two-digit numbers. There’s number 39, number 27, and
number 35. Let’s try putting these numbers in
ascending order, starting with the smallest and going up to the largest. To do this, we need to compare the
number of tens and ones in each number. Let’s start with the blue front
door. We can model the number 39 using
three tens and nine ones. Our second number is 27. We can show the number 27 by using
two tens and seven ones. And then finally, we can model the
number 35 out of three tens and five ones.
Now that we’ve modeled each number,
we can compare the tens and the ones together. What should we start by comparing,
the tens or the ones? Well, which do you think is more
important, which is larger, a ten or a one? Of course, a ten is larger than a
one. They’re worth more, so they’re more
important. We always compare the tens
first. How many tens are in each of our
numbers? We can see three tens, two tens,
and then another number with three tens. If we compare these numbers, we can
see that one of them is definitely the smallest number. Can you see which one it is?
The number 27 only has two tens,
whereas the other two numbers have three. So if we’re going to put our front
doors in order from least to greatest, we need to start with the number 27. So, we can forget about the number
27 for now; we know where it belongs. We just need to compare the other
two numbers, 39 and 35. As we’ve said already, both of
these numbers have three tens. So, we can’t split them up. We need to look at the ones. The number 39 has nine ones, and
the number 35 has five ones. Now, can we compare these
numbers?
Well, we know that five is less
than nine. So if we’re ordering our house
numbers from smallest to largest, number 35 will come before number 39. Our three numbers in ascending
order are 27, 35, and 39. Remember what we did to put the
numbers in order? We compared the tens first. And then because some of the tens
were the same, we then compared the ones. Let’s practice what we’ve learned
now. We’re gonna try answering some
questions where we have to order some two-digit numbers.
Look at these numbers. 41, 62, 34. Which is the greatest number? Which is the smallest number?
We can see three two-digit numbers
here. And they’re shown in two different
ways; they’re shown as a number but also using tens and ones. We’ve got the number 41, 62, and
34. And we’re asked two questions about
these numbers. Which of them is the greatest
number? In other words, which is
largest? And then, which is the smallest
number? You know, if we put these numbers
in order, say, from greatest to smallest, we’d be able to spot which number was the
greatest and which was the smallest. Why don’t we try doing that?
Now, when we put two-digit numbers
in order, we need to compare the tens and the ones. A ten is worth a lot more than a
one. So, we need to compare the tens
first; they’re more important. The number 41 contains four
tens. There are six tens in 62, and there
are only three tens in the number 34. The number of tens here are all
different. We don’t even need to look at the
ones. We could put these numbers now in
order. Which is the largest number? Well, six tens is larger than four
tens and is also larger than three tens.
So, if we’re putting our numbers in
order from greatest to smallest, we need to start with the number 62. We’re now left with 41 and 34. Which is the next largest number of
tens? Well, we know that four tens is
greater than three tens. So, 41 is the next largest number
in our list. And this means the smallest number
must be 34. This is the number with the least
amount of tens. Now, we’ve compared the tens. All we need to do is to use our
order to answer the two questions.
The greatest number here is 62;
it’s the number with the most tens. And the smallest number here is the
number 34; this is the number with the least tens.
Write the following numbers in
descending order: 25, 43, 27, and 75.
In this problem, we’ve been given
four two-digit numbers, and we’ve been asked to write them in order. But not just any order, we need to
write them in descending order. Now, when something descends, it
goes downwards. And so, when we put numbers in
descending order, they need to go downwards too. In other words, we need to put the
numbers in order from greatest to least. And we can do this by comparing the
number of tens and, if we need to, the number of ones too. To begin with, let’s model these
numbers out of tens and ones.
We can model the number 25 out of
two tens and five ones. The number 43 is made up of four
tens and three ones. The number 27 can be modeled using
two tens and seven ones. And the number 75 is made up of
seven tens and five ones. And remember, we need to put our
numbers in descending order from greatest to least. And to do this, we need to compare
the tens and, if we have to, the ones too. Let’s start by comparing the
tens. Can we see which number is the
greatest?
25 contains two tens. 43 contains four tens. There are two tens in 27. And there are seven tens in 75. If we look at these amounts, we can
see that seven tens is the greatest number of tens. 75 is the greatest number. Now that we know it comes first in
our order, we can forget about it. We just need to think about the
numbers 25, 43, and 27. Which is the next largest
number? Well, we know that four tens in 43
is greater than two tens. And both of the other numbers have
two tens. So, we can write number 43 as the
second number in our order.
Now, all we need to do is to
compare the numbers 25 and 27. Which is the largest number out of
25 and 27? Well, it’s no good comparing the
tens; both numbers have two tens. We need to compare the ones. 25 contains five ones, but 27
contains seven ones. And seven is greater than five. So, we know that 27 is greater than
25. We’ve put these four two-digit
numbers in descending order from greatest to least. And that order is 75, 43, 27,
25.
So, what have we learned in this
video? We’ve learned how to order numbers
up to 100 by comparing the tens and, when we’ve needed to, the ones.
