2.  Importance: to ensure the accuracy of our measurements  To make sure we tell others only what we actually know based on our equipment and it’s limitations  Significant figures: all the numbers actually measured plus one that is estimated

3.  Non zeros are always significant:  1.23456 has 6 sig figs  Zeros within a number are always significant. Both 4308 and 40.05 contain four significant figures.  Zeros that do nothing but set the decimal point are not significant.  470,000 has 2 significant figures.  0.00000000098 has 2 sig figs  Trailing zeros that aren't needed to hold the decimal point are significant.  4.00 has 3 significant figures.  0.0000050 has 2 significant figures

4.  The number of decimal places in the answer is equal to the number of decimal places in the quantity with the smallest number of decimal places  1. 2 3 + 4. 5 6 7 = 5. 8 0

5.  The LEAST number of significant figures in any number of the problem determines the number of significant figures in the answer.  2 x 10.0 = 20  66 / 2 = 33 = 30