Chapter 10: Percents Box 1 Rules for Manipulating Percents 1.To convert a percent to its decimal equivalent move the decimal point two places to the left. examples: 10% = % = % = To change a decimal to a percent, move the decimal point two places to the right and add a % sign. examples: 0.10 = 10% 0.87 = 87% 1 = 100%

Chapter 10: Percents Box 1 Rules for Manipulating Percents (continued) 3.To change a percent to a fraction, write the percent as a fraction with a denominator of 100. examples: 30% = 30/ % = 1.5/ % = 100/100 = 1

Chapter 10: Percents Box 1 Rules for Manipulating Percents (continued) 4. To change a fraction to a percent: Strategy 1: Use the logic of proportions Change 50/75 to a percent a. Set the problem up as a proportion equation ? =

Chapter 10: Percents Box 1 Rules for Manipulating Percents (continued) 4. To change a fraction to a percent: Strategy 1: Use the logic of proportions b. Cross multiply and divide ? = 66.66….. so 50/75 ≈ 66.67%

Chapter 10: Percents Box 1 Rules for Manipulating Percents (continued) 4. To change a fraction to a percent: Strategy 2: Convert the fraction to its decimal equivalent and then move the decimal two places to the right and add a % sign. a.Change the fraction to a decimal: 50/75 ≈ b. Change the decimal to a percent: ≈ 66.67%

Chapter 10: Percents Box 1 Rules for Manipulating Percents (continued) 5. To find a percentage of a particular number convert the percent to its decimal equivalent and multiply the decimal times the number of interest. Example: to find 45% of 900 a.Convert the percent to a decimal: 45% = 0.45 b. Multiply the decimal times the number of interest: 0.45 X 900 = 405

Chapter 10: Percents An Application of Percents: Percent Error of a Micropipette first, place an empty microcentrifuge tube on an analytical balance and push the “zero” or “tare” button empty microfuge tube “zero” button

Chapter 10: Percents An Application of Percents: Percent Error of a Micropipette look on thumb plunger for range range should be µl on plunger

Chapter 10: Percents An Application of Percents: Percent Error of a Micropipette set to 500 µl by turning plunger install a blue disposable tip

Chapter 10: Percents An Application of Percents: Percent Error of a Micropipette press plunger to first stop (not all the way down!) insert tip just beneath surface of liquid

Chapter 10: Percents An Application of Percents: Percent Error of a Micropipette slowly let plunger go all the way up to bring up liquid don’t insert tip too deep! very amateur!

Chapter 10: Percents An Application of Percents: Percent Error of a Micropipette weigh the water in the tared microfuge tube place tip in tared microfuge tube and slowly push plunger all the way down to second stop

Chapter 10: Percents An Application of Percents: Percent Error of a Micropipette % Error = X 100% true value – average measured value true value Do the procedure at least three times and calculate the average weight. This value will go here. 500 mg ( g) is the true value