1. How to Calculate Answers using Significant Figures

3. IT’S EASY! IT’S FAST! Two Rules are used: One for Adding & Subtracting
One for Multiplying & Dividing

4. When adding or subtracting
Note accuracy of measurements
(nearest .1? .01? .001?)
Answer can be no more accurate than the LEAST accurate number
that was used to calculate it.

5. For Example:
5.50 grams
grams
14.1 grams

6. OR ml ml
2.39 ml --> 2.4 ml

7. When multiplying or dividing
You must COUNT significant figures
The answer can have only AS MANY
significant figures as the LEAST of the numbers used to get it

8. Multiplication /Division
5.058 x 3.20

9. Multiplication /Division
5.058cm x 3.20cm
= cm2

10. Multiplication /Division
5.058cm x 3.20cm
= cm2
= 16.2cm2

11. Now let’s do some math..... (round answers to correct sig figs!)
g g
answer: 6.55 g
Did you need to count sig figs? NO!

12. Try this one.... 4.80 ml - .0015 ml answer: 4.80 ml
(one might say .0015
is insignificant
COMPARED TO 4.80)

13. Now try these... 5.0033 g / 5.0 ml answer: 1.0 g/ml
Did you have to count sig figs?
YES!

14. Here’s a tougher one..... 3.0 m/s x 60 s/min x 60 min/hr =
answer: m/hr --> m/hr
Note: standard conversion factors never limit significant figures--
instruments and equipment do.

15. THAT’S ALL THERE IS TO IT!
Use least accurate measurement when adding and subtracting
Count sig figs when multiplying and dividing