Subtracting decimals
Subtracting decimals using the column method is exactly the same as subtracting whole numbers.
You just have to make sure that the decimal points line up, so the place values of the digits are all the same.
Let's take a look at this method for subtracting decimals using some examples.
Example 1
What is 12.34 鈥 10.5?
Can you see that 12.34 has two digits after the decimal point; however, 10.5 only has one?
It鈥檚 always a useful idea to make sure both numbers have the same amount of digits after the decimal point.
10.5 doesn鈥檛 have any hundredths so you can represent that by including a 0 in the hundredths column.
Now starting from the hundredths column, begin subtracting鈥
Oh no! You can鈥檛 subtract 5 tenths from 3 tenths, so you have to exchange (or 鈥渂orrow鈥) from the ones column.
Now you have exchanged 1 one for 10 tenths, you can solve 13 tenths minus 5 tenths.
Remember, you now have to reduce the number of ones to represent this exchange.
Let's continue with the subtraction鈥
For the rest of the subtraction, you don鈥檛 have to exchange any more so subtracting the rest of the digits is straightforward.
So, 12.34 鈥 10.5 = 1.84
Example 2
What is 145.2 鈥 134.19?
First, make sure both numbers have the same amount of decimal places and the decimal points are lined up.
Now starting from the hundredths column, begin subtracting鈥
You cannot take 9 hundredths away from 0 hundredths, so you must exchange 1 tenth for 10 hundredths and then reduce the amount of tenths.
Now let's continue with the subtraction鈥
You do not have to exchange any more numbers in the subtraction, so you can easily subtract the rest of the digits.
Therefore:
145.2 鈥 134.19 = 11.01
Activity
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