For example, let's say you have to add the numbers 1.121, 48.00679392, and
6.3457:

1.121 + 48.00679392 + 6.3457 = 55.47349392

But, because 1.121 has only three decimal places, the answer must actually be:
55.473, since it is at the third decimal place that uncertainty begins to enter
the picture.

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Significant Figures in Multiplication and Division

The rule governing multiplication and division of significant figures is
slightly different than that for addition and subtraction, but just as simple:

The final value can only have as many significant figures as the original value
with the least significant figures.

For example, consider the following situation: a scientist needs to calculate a
constant value, K, based on the following equation:

K = (D x E) / B

where B, D and E are measured values that the scientist observed (weight,
volume, temperature, pressure).

B=6.00 g
D= 22 C
E= 22.457 mL

22.457 mL has 5 significant figures and 22 C has 2 significant figures. The
number that the calculator gives is 82.34233... However this has 7 significant
figures and none of the measurements were this accurate. In fact, we must
reduce the answer to only two significant figures, since that's how many 22 has.
The answer, K, must be truncated to 82 ml C/g to reflect the 2 significant
figures in the D value.