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multiplied by a number with four significant figures, the computed result will have only three significant
figures. Even if a calculator computes eight digits, most of them will be meaningless in terms of their physical
For example, the density of an object is its mass divided by its volume. The density of an object with a
mass of 2.157 g that occupies 1.66 cm3 can be known to only three significant figures:
= 1.29939759 g/cm3 ← calculator result
1.66 cm 3
= 1.30 g/cm3 ← rounded off Rounding Off Numbers. A number is rounded off to the desired number of significant figures by
dropping one or more digits to the right. The following rules should be observed when rounding off numbers:
3. When the first digit dropped is less than 5, the last digit retained remains unchanged. Thus, 4.2643 rounded
to three significant figures becomes 4.26.
When the first digit dropped is equal to or greater than 5, the last digit retained is increased by 1. Thus,
2.38 and 2.35 rounded to two significant figures both become 2.4....
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This note was uploaded on 09/15/2009 for the course CHEM 102 taught by Professor Bastos during the Spring '08 term at Adelphi.
- Spring '08