1. Significant Figures
All non-zero digits are significant (2.45 has 3 SF)
Zeros between (sandwiched)non-zero digits are significant
(303 has 3 SF)

2. 3. Zeros to the left of all non-zero digits are NEVER significant. (0
3. Zeros to the left of all non-zero digits are NEVER significant ( has 2 SF and has 3 SF)
Zeros to the right of all non-zero digits are only significant if they are also to the right of the decimal
(250 has 2 SF and has 5 SF)

3. Counting numbers have infinite significant figures
(21 students has infinite SF)
6. Exactly defined quantities have infinite significant figures
(100 cm = 1 m -both terms have infinite SF)

4. Practice
1000
3 SF
1 SF
6 SF
7 SF

5. Adding and Subtracting with Significant Figures
The answer should have no more decimal places than the number in the problem with the least decimal places cm cm cm = 15.5 cm

6. Practice m m m g g g ml ml ml

7. Multiplying and Dividing
The answer must be rounded to the same number of significant figures as the number in the problem with the least significant figures.
7.83 kg
x 2.1 kg
kg = 16 kg

8. g
12.4 cm3
= g /cm3
= g/ cm3

9. Practice
( m) (21.4 m) = m2 = m2 = 1.58 x 106 m2
(691 g / cm3) = g / cm3 = g / cm3 = 1.73 x 106 g / cm3

10. Rounding Select the place you want to round to: 26.3495
Look at the place after the one you want to round to:
If < 5 round down
If ≥ 5 round up
26.35

11. Practice 705.3998 to 4SF 0.00638114 to 3SF 6.037 x 10-8 to 3SF
705.4 (7.054 x 102) (6.38 x 10-3) 6.04 x (7.8 x 103)