2. Lesson 6.7: Box-and-Whisker Plots
Algebra I

3. Definitions
Box-and-Whisker Plot: A data display that divides a set of data into four parts.
Second Quartile [Middle Quartile]: The median of the data set.
First Quartile [Lower Quartile]: The median of the lower half of the data set.
Third Quartile [Upper Quartile]: The median of the upper half of the data set.

4. Example
Find the first, second and third quartiles of the following data. 58 75 89 98 67 73 81 93 77 85 92 78

5. Check for Understanding
Find the first, second and third quartiles of the following data. 22 21 17 16 18 27

6. Drawing a Box-and-Whisker Plot
You need to know 5 values in order to construct a Box-and-Whisker Plot:
Least Number (Minimum)
First Quartile (Lower Quartile)
Second Quartile (Middle Quartile)
Third Quartile (Upper Quartile)
Greatest Number (Maximum)

7. Drawing a Box-and-Whisker Plot
Draw a number line that includes the least and greatest number in the data set.
Plot your 5 values on the number line.
Draw a line from the least number to the greatest number below your number line. Plot your 5 points on this line
The “box” extends from the first to the third quartile. The “whiskers” connect the box to the least and greatest numbers.

8. Example
Q1=
Q2=
Q3=
MAX=
MIN= 58 75 89 98 67 73 81 93 77 85 92 78

9. Check for Understanding
Q1=
Q2=
Q3=
MAX=
MIN= 16 22 21 17 18 27

10. Why is a Box-and-Whisker Plot Useful?
Gives a visual representation of data
Easy to compare and contrast between different sets of data.

11. Example Precip. in Chicago over last 30 years
26.6
28.1
28.7
29.4
29.5
30.2
31.8
32.0
32.8
33.4
33.8
34.1
34.5
34.9
35.2
37.2
37.7
38.1
38.5
39.1
39.4
39.8
40.1
40.5
41.3
45.5
45.8
46.0
46.2
49.4
Precip. in San Diego over last 30 years
3.7
4.1
5.4
5.6
6.1
6.9
7.8
8.1
8.4
8.7
8.8
9.0
9.1
9.3
11.3
11.6
11.7
12.1
12.3
12.5
12.7
12.8
13.0
13.1
14.3
15.8
16.2
16.7
19.4

12. 0 10 20 30 40 50 Minimum 26.6 1ST Quartile 32.0 2ND Quartile 36.2
3RD Quartile
40.1
Maximum
49.4
Minimum
3.7
1ST Quartile
8.1
2ND Quartile
10.3
3RD Quartile
12.8
Maximum
19.4

13. Classwork: pg. 378 #1-10 (all)

14. Homework
Pg. 378 #11-23 (odd), #30
FROM 6.6:
Pg. 371 # 11, 13, 25, 27