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When adding numbers expressed using scientific notation, it is often useful to write the numbers using non‐standard coefficients to simplify the mathematical process.

For example, the number 4 242 can be written in any of the following ways and retains its original numerical value:

Only the last figure is standard scientific notation. However, if we were required to add the number 4 242 to 5.00 × 10² and give the answer in standard scientific notation, the following procedure could be used:

The example shows that the numbers are converted such that the exponent is common, i.e. 10² in this case, and then the numbers can be added.

Similarly, with numbers smaller than 1, the values are converted such that the exponents are common and added or subtracted in the normal manner. The exponent remains unchanged.

For example:

In this example the numbers are exact, that means we know them precisely. For example the number of people in a room. We therefore don’t need to give the answer to a specific number of significant figures as, effectively, the number of significant figures is infinite.

This answer must be rounded, as we only know the original values to an accuracy of three significant figures.