Significant figures are the number of digits of a number that are known with a certain degree of precision, for example, a burette reading of 15.25 cm3 has 4 significant figures, while the reading of 0.084 g for the mass of an object has 2 significant figures. The rules that determine the number of significant figures in a number are:
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- Zeros preceding the first non-zero digit of a number are not significant, e.g. 0.084 and 0.1 have 2 and 1 significant figures respectively.
- Zeros in between non-zero digits of a number are significant, e.g. 1005 and 1.005 have 4 significant figures each.
- Zeros trailing the last non-zero digit of a decimal are significant, e.g. 2.3400 and 0.2300 has 5 and 4 significant figures respectively.
- Zeros trailing the last non-zero digit of a positive or negative integer may or may not be significant, e.g. 2500 may have 2 or 3 or 4 significant figures. To avoid confusion, such numbers should be expressed in standard form, e.g. 2.5 x 103, 2.50 x 103 and 2.500 x 103 have 2, 3 and 4 significant figures respectively.
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