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Significant figure
 a digit that is reliably known.
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Ex: 6.2 has 2 sig figs. The hundredth place is not reliably known and, thus, not reported.

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The easiest way to determine sig figs in a number is to write the number in scientific notation.
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0.00620 = 6.20 x 10 -3
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The trailing zero is reliably known, so it is
SIGNIFICANT.
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The number of significant figures is the number of digits when written in sci notation.

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The number of sig figs does not equal the number of decimal places.
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In whole numbers, trailing zeroes are not sig figs.
Ex: 320,000 is 3.2 x 10 5
It has 2 sig figs.
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Changing units may shift the decimal points but it doesn’t change the number of sig figs.

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When multiplying/dividing (or taking roots), the number of sig figs in the answer should match the number of sig figs of the least precise number in the calculation.
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When adding/subtracting, the number of sig figs in the answer should match the smallest amount of decimal places of any number in the calculation.

• It’s fine to keep extra numbers around in the intermediate steps, but your final answer MUST be accurate in terms of significant figures.
• Otherwise, you’ve performed magic and have something more accurate that we can verify.

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The volume of a piece of Al is 4.44 x 10 -4 m 3 . Given a density of 2.7 x10 3 kg/m 3 , what is the total mass of the piece of Al? (mass = density x volume)

m= 4.44 x 10 -4 m 3 (2.7 x10 3 kg/m 3 ) m= 1.199 kg m= 1.2 kg

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If we have a second mass of Al, measured to be 6.47 kg, how much total Al do we have?

6.47 kg + 1.2 kg
= 7.7 kg