Significant Figures

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Example 1

Three students weigh an item using different scales. These are the values they report:

a. 20.03 g
b. 20.0 g
c. 0.2003 kg

How many significant figures should be assumed in each measurement?

Solution

a. 4.
b. 3. The zero after the decimal point is significant because it indicates that the item was weighed to the nearest 0.1 g.
c. 4. The zeros at the left are not significant. They are only present because the mass was written in kilograms rather than in grams. The values '20.03 g' and '0.02003 kg' represent the same quantities.

Answer

In addition to the solution presented above, be advised that the correct answers to have been obtained very quickly by expressing the masses in scientific (exponential) notation:

20.03 g = 2.003 x 10¹ g (4 significant figures)
20.0 g = 2.00 x 10¹ g (3 significant figures)
0.02003 kg = 2.003 x 10^-2 kg (4 significant figures)

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