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SECTION 1 - DECIMALS
The most common use of decimals is probably in the cost of items. If you’ve
worked in a shop or pub, you’re probably already familiar with working with
decimals.
Addition and Subtraction
The key point with addition and subtraction is to line up the decimal points!
Example 1
2.67 + 11.2 = 2.67
+11.20 → in this case, it helps to write 11.2 as 11.20
13.87
Example 2
14.73 – 12.157 = 14.730 → again adding this 0 helps
- 12.157
2.573
Example 3
127.5 + 0.127 = 127.500
+ 0.127
127.627
Multiplication
When multiplying decimals, do the sum as if the decimal points were not there, and
then calculate how many numbers were to the right of the decimal point in both
the original numbers - next, place the decimal point in your answer so that there
are this number of digits to the right of your decimal point.
Example 4
2.1 x 1.2.
Calculate 21 x 12 = 252. There is one number to the right of the decimal in each of
the original numbers, making a total of two. We therefore place our decimal so
that there are two digits to the right of the decimal point in our answer.
Hence 2.1 x 1.2 =2.52.
Always look at your answer to see if it is sensible. 2 x 1 = 2, so our answer should
be close to 2 rather than 20 or 0.2 which could be the answers obtained by putting
the decimal in the wrong place.
Example 5
1.4 x 6
Calculate 14 x 6 = 84. There is one digit to the right of the decimal in our original
numbers so our answer is 8.4
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