1. Notes 51
Histograms

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

3. Additional Example 1A: Analyzing Histograms
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.
A. How many people sleep less than 9 hous per night?
Add the number of students in the 3-5 and 6-8 intervals.
= 78
78 people sleep less than 9 hous per night.

4. 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.
Interval
Frequency
Rank
(by weight)
3-5 25
1-25
6-8 53
26-78
9-11 17
79-95
12-14 5
96-100
Determine the interval of the 50th and 51st people.
The 50th and 51st persons’ hours are in the middle of the 6-8 interval. So, a good estimated is 7 hours.

5. Check It Out: Example 1
The histogram shows the results of a local 10K race. Use the histogram to answer each question.

6. 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?

7. Additional Example 2: Making a Histogram
The table below shows the number of hours students watch TV in one week. Make a histogram of the data.
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
Frequency
Number of Hours of TV
1–3 15
4–6 17
7–9 17

8. Additional Example 2 Continued
Step 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. 20 16 12 8 4
1–3
Frequency
Number of Hours of TV 15
4–6 17
7–9

9. Additional Example 2 Continued
Step 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. 20 16 12 8 4
1–3
Frequency
Number of Hours of TV 15
4–6 17
7–9
Because the intervals are equal, all of the bars should have the same width.
Caution!

10. Additional Example 2 Continued
Step 4: Label the axes and give the graph a title.
Hours of Television Watched 20 16 12 8 4
1–3
Frequency
Number of Hours of TV 15
4–6 17
7–9
Frequency
1–3
4–6
7–9
Hours

11. Check It Out: Example 2 6 7 8 9 1 2 3 4 5 Number of Pets
The table shows survey results about the number of household pet(s) students have at home. Make a histogram of the data. 6 7 8 9 1 2 3 4 5
Number of Pets