Ordering Numbers

Ordering Numbers

Your child may come across questions in their exam which may ask them to order numbers. This could be in descending order (from largest to smallest) or in ascending order (from smallest to largest).

Before starting this section with your child, make sure they are comfortable with place value.

Ordering Decimals

Ordering decimals works in the same way as ordering whole numbers. We look at each column in turn starting with the left most column and compare the digits.

Example: Put the following numbers in order from smallest to largest.

1.45,1.54,0.44,1.051.45,,,1.54,,,0.44,,,1.05

First, we look at the left most column, in this case the units column and compare the digits. Three of the numbers have a 1textcolor{red}{1} in the units column and one of the numbers has a 0textcolor{red}{0} in the units column.

1.45,1.54,0.44,1.05textcolor{red}{1}.45,,,textcolor{red}{1}.54,,,textcolor{red}{0}.44,,,textcolor{red}{1}.05

As 0textcolor{red}{0} is less than 1textcolor{red}{1}, 0.440.44 is the smallest number and will be listed first.

With the three remaining numbers look to the tenths column or the first decimal place.

1.45,1.54,1.051.textcolor{red}{4}5,,,1.textcolor{red}{5}4,,,1.textcolor{red}{0}5

Comparing these values we find that 0textcolor{red}{0} is the smallest then 4textcolor{red}{4} and finally 5textcolor{red}{5} is the largest. With this information we can order the rest of the numbers.

So, our final answer is:

0.44,1.05,1.45,1.540.44,,,1.05,,,1.45,,,1.54

Example 1: Ordering from Largest to Smallest

If your child is asked to order a set of numbers in descending order then they should order the numbers from largest to smallest.

Example: Write the following numbers in order from largest to smallest.

98,102,118,8998,,,102,,,118,,89

First, we need to look at how many digits each number has. 102102 and 118118 have three digits and 9898 and 8989 have two digits.

When there are no decimals involved this means that the numbers with three digits are larger than the ones with two digits.

Next, let’s look at the numbers with three digits to find which one is the largest.

102,118textcolor{red}{1}02,,,textcolor{red}{1}18

Both numbers have a 1textcolor{red}{1} in the hundreds column, this doesn’t help so we move to the right and look at the digits in the tens column.

102,1181textcolor{red}{0}2,,,1textcolor{red}{1}8

1textcolor{red}{1} is larger than 0textcolor{red}{0} so 118118 is the largest number followed by 102102.

Then we can do the same process to find the larger two digit number.

98,89textcolor{red}{9}8,,,textcolor{red}{8}9

9textcolor{red}{9} is larger than 8textcolor{red}{8} so 9898 is larger than 8989.

So, our final answer is:

118,102,98,89118,,,102,,,98,,,89

Ordering Numbers Example Questions

Question 1: Write the following numbers in order from smallest to largest.

656,555,556,665656,,,555,,,556,,,665

[1 mark]

All numbers have three digits.

Look at the digits in the hundreds columns.

656,555,556,665textcolor{red}{6}56,,,textcolor{red}{5}55,,,textcolor{red}{5}56,,,textcolor{red}{6}65

As 6textcolor{red}{6} is larger than 5textcolor{red}{5}, 656656 and 665665 are larger than 555555 and 556556.

Next, looking at the tens column to find the largest.

656,6656textcolor{red}{5}6,,,6textcolor{red}{6}5

So, 665665 is the largest number followed by 656656.

Now comparing the digits in the tens column for the remaining numbers.

555,5565textcolor{red}{5}5,,,5textcolor{red}{5}6

Both digits are the same so we move on to compare the digits in the units column.

555,55655textcolor{red}{5},,,55textcolor{red}{6}

From this we can deduce the correct answer is:

555,556,656,665555,,,556,,,656,,,665

Question 2: Write the following numbers in order from largest to smallest.

34.2,33.1,33.3,3434.2,,,33.1,,,33.3,,,34

[1 mark]

These numbers are in the same format of two digits before the decimal point and one digit after the decimal point except for 3434. We can rewrite this as 34.034.0 so that it matches up and is easier to compare.

34.2,33.1,33.3,34.034.2,,,33.1,,,33.3,,,34.0

Now we can approach the question as we normally would.

Looking at the tens column first.

34.2,33.1,33.3,34.0textcolor{red}{3}4.2,,,textcolor{red}{3}3.1,,,textcolor{red}{3}3.3,,,textcolor{red}{3}4.0

They are all the same digit so we will need to look to the units column.

34.2,33.1,33.3,34.03textcolor{red}{4}.2,,,3textcolor{red}{3}.1,,,3textcolor{red}{3}.3,,,3textcolor{red}{4}.0

From this we can see that 34.234.2 and 34.034.0 are larger than 33.133.1 and 33.333.3

Then, we need to look at the tenths column to find the largest number.

34.2,34.034.textcolor{red}{2},,,34.textcolor{red}{0}

So, the largest number is 34.234.2 followed by 34.034.0.

Next compare the digits in the tenths column to find which is the smallest.

33.1,33.333.textcolor{red}{1},,,33.textcolor{red}{3}

So, our final order becomes:

34.2,34,33.3,33.134.2,,,34,,,33.3,,,33.1

Question 3: Farah sees the following price list at a coffee shop.

List the items in order of cheapest to most expensive.

[2 marks]

Let’s unpick what the question is asking us to do!

We have a list of prices (which are just decimals) and we want to order them from cheapest to most expensive, so in other words smallest to largest.

First, list the numbers out.

2.15,2.51,3.05,2.552.15,,,,2.51,,,3.05,,,2.55

All of the numbers have the same number of digits before the decimal point and the same number of digits after the decimal point.

Next, look at the units column.

2.15,2.51,3.05,2.55textcolor{red}{2}.15,,,textcolor{red}{2}.51,,,textcolor{red}{3}.05,,,textcolor{red}{2}.55

From this we can identify that 3.053.05 is the largest (or most expensive).

Then let’s use the tenths column for the rest of our numbers.

2.15,2.51,2.552.textcolor{red}{1}5,,,2.textcolor{red}{5}1,,,2.textcolor{red}{5}5

This tells us that 2.152.15 is the smallest or the cheapest.

We will have to look at the hundredths column to distinguish between the final two prices.

2.51,2.552.5textcolor{red}{1},,,2.5textcolor{red}{5}

So, the correct order is:

£2.15,£2.51,£2.55,£3.05pounds 2.15,,, pounds 2.51,,, pounds 2.55,,, pounds 3.05

Or ordering the items like asked in the question gives us the final answer of…

Cup of tea, Cup of coffee, Lemonade, Milkshake