# Lesson Video: Ordering Two-Digit Numbers Mathematics • 1st Grade

In this video, we will learn how to order numbers up to 100 by comparing the number of tens and ones.

10:52

### 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.

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