Skills 5, 6, 7

2.1 Displaying Distributions With Graphs
Counts- the total number
Rates- percents and proportions—easier to understand than numbers (easier for comparison)
Distribution-the way something is spread out among a group
Example—with a variable and how it is distributed, values of the variable and how often it uses each value
Round off errors- the difference between the approximated number and its exact value
Example 2.1—Education level in the United States: a bar graph
Bar graph- a diagram with variables which are represented by height and length of lines or rectangles of equal width
- Good visual method of comparing data
- Easier to do by hand—more accurate
Example 2.2—Education level in the United States: a pie chart
Pie Chart—a circle which is divided into parts which represent a percent of the whole
To make a pie chart you make a circle and, using a protractor to accurately show the angles, you fill in the percents given. If you are given a percent then you must convert it to degrees. A circle is 360 degrees so an example of converting percent to degrees would be:
If you were given 22.8% then you would do-- .228 X 360= 82
Example 2.3—Hang up and drive!
Even though you always have the option of using a bar graph you cannot always use a pie chart. For example in the experiment given they are testing the percent of people that use cell phones while driving in each region. Because regions are being used there is no whole, the experiment only compares four separate quantities.
Practice Problems—
(found on page 40)
2.1 Martial status—In the Statistical Abstract of the United States we find these data on the marital state of adult American women as of 2007


Marital Status Count (thousands)
Never Married 25,262
Married 65,128
Widowed 11,208
Divorced 13,210
Total 114,807


a) How many women were not married in 2007?
b) Make a bar graph to show the distribution of marital status.
c) Would it also be correct to use a pie chart? If so, make a pie chart for these data

2.2 Consistency? Refer to the previous exercise. What is the sum of the counts for the four marital status categories? Why is this sum not equal to the total given in the table?

2.3 College Freshman—a survey of college freshman asked what field they planned to study. The results: 25.2% arts and humanities, 19.3% business, 7.1% education, 16.6% engineering and science, 7.8% professional and 15.3% social science.
a) What percent plan to study fields other than those listed?
b) Make a graph that compares the percents of college freshman planning to study various fields.

You got the next blog Geoff! Congrats!