1. Percentages and Percent Error

2. Calculating Percents Puts everything on a basis of 100. Percent (%) = # of items of interest x 100 total number of items

3. Sample Calculation Our class contains 33 students. Of these, 18 are men and 15 are women. What is the percentage of women in the class? What is the percentage of men in the class?

4. Calculations % men = 18 x 100 = 54.5454545455 33 % women = 15 x 100 = 45.45454545 33

5. Percents Help Us Compare You are offered two samples of gold. –First weighs 57 g and contains 43% Au. –Second weighs 39 g and contains 66% Au Which would you rather have?

6. 57 g @ 43% Au 57 g sample x 43 g Au. = 25 g 100 g sample

7. 39 g @ 66% Au 39 g sample x. 66 g Au = 26 g Au 100 g sample

8. Choice of units is arbitrary 77% =. 77 oz Au. =. 77 g Au. 100 oz sample 100 g sample

9. % as a Conversion Factor Try Problem 3.106 in text Try Problem 3.108 in text

10. Percent Error % er = measured error - accepted value x 100 accepted value

11. Try It! Sue measured the density of Pb as 11.26. The generally accepted value is 11.34. What was Sue’s percent error?

12. Assignment Read 3.10 Do Assigned Problems ONLY in the 3.97-3.112 range

13. Sig Figs in Means and Std Devs Test Scores MeanDeviationDev 2 988711120 72.587-14.5=15225=230 87 00 83.387-3.714 94.5877.556 87.06 420/4=105=100 10 (10.2)