Histograms

*Notes 51

Vocabulary

Histogram- a bar graph that shows the frequency of data within equal intervals. There is no space between the bars in a histogram.

The histogram shows the results of a survey asking people the number of hours they sleep per night. Use the histogram to answer each question.

Additional Example 1A: Analyzing Histograms

A. How many people sleep less than 9 hous per night?

Add the number of students in the 3-5 and 6-8 intervals.

23 + 58 = 7878 people sleep less than 9 hous per night.

Additional Example 1B: Analyzing Histograms

B. What is the approximate median number of hours people sleep per night?

Since 100 people were surveyed, the median is the mean of the 50th and 51st persons’ hours.

The 50th and 51st persons’ hours are in the middle of the 6-8 interval. So, a good estimated is 7 hours.

Interval Frequency Rank (by weight)

3-5 25 1-25

6-8 53 26-78

9-11 17 79-95

12-14 5 96-100Determine the interval of the 50th and 51st people.

The histogram shows the results of a local 10K race. Use the histogram to answer each question.

Check It Out: Example 1

Check It Out: Example 1 Continued

A. How many runners completed the race in less than 50 minutes?

B. What is the approximate median time people ran the race?

The table below shows the number of hours students watch TV in one week. Make a histogram of the data.

Additional Example 2: Making a Histogram

Step 1: Make a frequency table of the data. Be sure to use equal intervals. 6 ///

7 //// ////

8 ///

9 ////

1 //

2 ////

3 //// ////

4 //// /

5 //// ///

Number of Hours of TV

1–3

FrequencyNumber of Hours of TV

15

4–6 17

7–9 17

Additional Example 2 ContinuedStep 2: Choose an appropriate scale and interval for the vertical axis. The greatest value on the scale should be at least as great as the greatest frequency.

1–3

FrequencyNumber of Hours of TV

15

4–6 17

7–9 17

20

16

12

8

4

0

Additional Example 2 ContinuedStep 3: Draw a bar graph for each interval. The height of the bar is the frequency for that interval. Bars must touch but not overlap.

1–3

FrequencyNumber of Hours of TV

15

4–6 17

7–9 17

20

16

12

8

4

0

Because the intervals are equal, all of the bars should have the same width.

Caution!

Additional Example 2 ContinuedStep 4: Label the axes and give the graph a title.

1–3

FrequencyNumber of Hours of TV

15

4–6 17

7–9 17

20

16

12

8

4

01–3 4–6 7–9

Hours of Television Watched

Freq

uen

cy

Hours

The table shows survey results about the number of household pet(s) students have at home. Make a histogram of the data.

Check It Out: Example 2

6

7

8

9

1

2

3

4

5

Number of Pets