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Subtract double digit numbers with decimals in tenths or hundredths


We've started looking at how to subtract numbers with decimal values. In this chapter, we're going to build on this knowledge and look at how to do this with larger numbers.


Subtracting a whole number from a number with a decimal

There are a few strategies we can use to subtract a whole number from a number with a decimal. However, it's always important to remember the value of each digit when doing this. One thing we can do is rename our number, say $5$5, to $5.00$5.00, and this doesn't change the value of the number. We can then line our two numbers up under each other, as both have two decimal places. Then it's like we're subtracting a two decimal number from another two decimal number.  


A whole number, such as $48$48, has the same value as $48.00$48.00


Regrouping then subtracting

Sometimes we need to regroup, or rename, some of our values before we can subtract.  We use the same process as we use with whole numbers, so using place value columns can really help.  


If it's a little daunting to solve a decimal subtraction across your page, use a place value table, or columns, or even grid paper. Be sure to line up the decimal point!


Worked examples

Question 1

Evaluate $38.32-19.67$38.3219.67

Question 2

Evaluate $97.32-34.12$97.3234.12

Question 3

Evaluate $78.93-33.01$78.9333.01 by doing the following.

  1. Round $78.93$78.93 and $33.01$33.01 to the nearest whole number and find the difference between these rounded values.

  2. Now evaluate $78.93-33.01$78.9333.01

  3. Calculate the difference between the rounded result and the precise result.

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