Percentages and Percent Error

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

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?

Calculations % men = 18 x 100 = % women = 15 x 100 =

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?

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

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

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

% as a Conversion Factor Try Problem in text Try Problem in text

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

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

Assignment Read 3.10 Do Assigned Problems ONLY in the range

Sig Figs in Means and Std Devs Test Scores MeanDeviationDev =15225= /4=105= (10.2)