Idiot\'s Guides Basic Math and Pre-Algebra

266 Part 4: The State of the World

Histogram .....................................................................................................................................

There’s another type of graph that, at first glance, may look a lot like a bar graph, but there are

some key differences. The graph is called a histogram. It does use bars, but instead of represent-

ing different categories, this graph tells you how often a particular number or measurement

showed up in the data. A histogram is an example of a frequency graph. It tells you how often,

how frequently, a particular value occurs.

If you surveyed a group of people and asked how many pets they owned, you would likely get

answers ranging from 0 to perhaps 5 or 6. It’s also likely that there will be more than one person

giving each of those answers. You could draw a histogram to show how many people gave each

answer.

Notice that in the histogram the bars are

touching, but in the bar graph there was

space between them. That’s because in a

bar graph the categories on the horizontal

axis are separate from one another. In the

histogram, the horizontal axis has all the

possible answers in numerical order, and

every number on that axis is counted in one

of the bars. Each bar picks up just where

the last one left off, and no value on the

horizontal axis is left out.

40

35

25

20

15

10

5

0

123456

Number of Pets

Circle Graph ...............................................................................................................................

Circle graphs, sometimes called pie charts, are visual aids that show a circle broken into wedges,

in much the way you would slice a pie or cake.

When to Use It

Circle graphs are used to represent quantities as fractions of a whole. When you have several

numbers that all combine to make up one thing, a circle graph may be a good way to show that.

If you know that you have 8 seniors, 5 juniors, and 2 sophomores on your team, you might use

a circle to represent the team, broken into three wedges. The size of each wedge corresponds to

the fraction of the team that comes from each class.