Review of Basic Mathematics

Rounding
When we round decimals to a certain number of decimal places we are replacing the
figure we have with the one that is closest to it with that number of decimal places.
An example: Round 1.25687 to 2 decimal places
1. Firstly look at the decimal place after the one you want to round to (in our
example this would be the third decimal place)
2. If the number in the next decimal place is a 6,7,8 or 9, then you will be rounding
up, so you add 1 to the number in the place you are interested in and you have
rounded. In our example the number in the third place is a 6 so we round up.
We change the 5 in the second place to a 6 and our rounded number is 1.26
3. If the number in the place after the one we are interested in is a 0,1,2,3 or 4 we
round down, i.e. we just write the number out as it is to the required number
of places.
4. If the number in the place after the one we are interested in is a 5, then we
need to look at what follows it. Cover the number from the beginning to the
place you are interested in, for example, suppose we are rounding 2.47568 to
three decimal places we look at just the 568 and we ask is that closer to 500 or
600. Since its closer to 600 we get a rounded number of 2.476
5. If only a 5 follows the place we are interested in then different disciplines have
different conventions for the rounding. You can either round up or down since
5 is exactly half way between 0 and 10.
Addition and Subtraction of Decimals
To add or subtract decimal numbers you should always remember to line up the
decimal point and then add or subtract normally. For example:
25 + 25.5+.025 + 2.25 and 36.25 − 6.475
25.000 + 36.250 −
25.500 6.475
0.025
2.250
29.775
52.775
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