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# Decimals, ratios, percentages, units and scientific notation

### Scientific notation

• Used to express very small or large numbers.
• Normally written as a number between $$0$$ and $$10$$ multiplied by a power of $$10$$.

For example:

• The braking stress of steel $$430\:000\:000~\mbox{Pa}$$ can be written as: $4.3\times 10^{8}\ \mbox{Pa}$
• The wavelength of red light $$0.000\:000\:644~\mbox{m}$$ can be written as: $6.44\times 10^{-7}~\mbox{m}$
• The mass of a virus:
$0.000\:000\:000\:000\:000\:000\:3~\mbox{kg}$
can be written as:
$3\times 10^{-19}~\mbox{kg}$