Chapter 10: PercentsBox 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% = 0.10 15% = 0.15 0.1% = 0.001

2. 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: PercentsBox 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% = 30/100

1.5% = 1.5/100 100% = 100/100 = 1

Chapter 10: PercentsBox 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

5010075

?=

Chapter 10: PercentsBox 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: PercentsBox 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 ≈ 0.6667

b. Change the decimal to a percent: 0.6667 ≈ 66.67%

Chapter 10: PercentsBox 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 900a.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: PercentsAn 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

emptymicrofuge tube

“zero” button

Chapter 10: PercentsAn Application of Percents: Percent Error of a

Micropipette

look on thumb plunger for range

range should be 100-1000 µlon plunger

Chapter 10: PercentsAn Application of Percents: Percent Error of a

Micropipette

set to 500 µl by turning plunger

install a blue disposable tip

Chapter 10: PercentsAn 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: PercentsAn Application of Percents: Percent Error of a

Micropipette

slowly let plunger go all theway up to bring up liquid

don’t insert tip too deep! very amateur!

Chapter 10: PercentsAn 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: PercentsAn 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 (0.5000 g) is the true value