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# Decimals, ratios, percentages, units and scientific notation

### Working with decimals

• Decimal fractions are commonly expressed using decimal notation $$(\cdot)$$.
• The same rules apply for addition and subtraction of whole numbers: calculate by lining up the numbers according to place value.
• To multiply and divide decimals: ignoring the decimal points, multiply the numbers as if they were whole numbers, then position the decimal point to give the same number of decimal places as in the question.
• For example, $$0.75$$ the numerator is $$75$$ and the implied denominator is $$10^{2} = 100$$, because there are two digits to the right of the decimal point.