lesson 6.7: box-and-whisker plots

Lesson 6.7: Box-and-Whisker Plots

Algebra I

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.

Example

• Find the first, second and third quartiles of the following data.

58 75 89 98 67 73 81

93 77 85 89 92 78 85

Check for Understanding

• Find the first, second and third quartiles of the following data.

22 21 1716 18 22 27

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)

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.

Example

58 75 89 98 67 73 81

93 77 85 89 92 78 85

Q1= Q2= Q3= MAX= MIN=

Check for Understanding

16 22 21 1716 18 22 27

Q1= Q2= Q3= MAX= MIN=

Why is a Box-and-Whisker Plot Useful?

• Gives a visual representation of data• Easy to compare and contrast between

different sets of data.

Example

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

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 9.1 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

Precip. in Chicago over last 30 years

Precip. in San Diego over last 30 years

0 10 20 30 40 50

Minimum 3.7

1ST Quartile 8.1

2ND Quartile 10.3

3RD Quartile 12.8

Maximum 19.4

Minimum 26.6

1ST Quartile 32.0

2ND Quartile 36.2

3RD Quartile 40.1

Maximum 49.4

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

Homework

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