Basically you should not include any more precision in the answer than is available in the question.
So if you have:
A = 1.2 / 2.3
the answer should not be quoted as 0.52173913
If we are rounding off the two input values, they might be anything from 1.15 to 1.25 and 2.25 to 2.35
Thus A can be anything from 1.15 / 2.35 = 0.4893617... up to 1.25 / 2.25 = 0.555555...
So in this case we can say only say the answer is about 0.52 (+/- 0.03)
Note the distinction between significant figures and decimal places.
In my example above the input values have 1 decimal place, but two significant figures,
(the output value has 2 significant figures and 2 decimal places).
It is unlikely that the input values are both at the extreme edges,
There is quite a sophisticated statistical analysis for error estimation (and thus provision of suitable numbers of significant figures)
However, as a pretty reliable rule of thumb,
the number of significant figures in the answer should not exceed the (minimum) number of significant figures in the question.
So the answer to A = 1.20 / 2.30 would be 0.522
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Last edited by Woody; Oct 12th 2017 at 06:29 AM.
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