Box-And-Whisker Plot

Box-And-Whisker Plot

Box-And-Whisker Plot

26, 17, 21, 23, 19, 28, 17, 20, 29

STEM

LEAF

1

7 7 9

2

0 1 3 6 8 9

KEY: 1|7 means 17

Median = 17, 17, 19, 20, 21, 23, 26, 28, 29

Median = 21

Lower quartile ( Q1) = 17, 17, 19, 20 begin with the smallest number

17 + 19 stop at the number just before the

2 median

Find the median of the data

Lower quartile = 18

Upper quartile (Q3) = 23, 26, 28, 29 begin with the first number after the 26 + 28 median to the right

2 Find the median of the data

Upper quartile = 27

Interquartile range = 27 - 18 Is the difference between the Upper

Quartile and the lower quartile. This tells how large the spread of data around the median is.

Interquartile range = 9

EX: Use the data below to answer the following questions.

73, 67, 75, 81, 67, 75, 85, 69

a) Arrange the data in order from least to greatest.

b) Find the median of the data.

c) Find the lower and upper quartile of the data

d) What is the interquartile range for the data?

e) Create a box-and-whisker plot for the data.



ACTIVITY #1

Technology Lab Recording Sheet; Holt Algebra 1 Section 10-3

ACTIVITY #2

Problem Solving; Data Distributions; Holt Algebra 1 Section 10-3

ACTIVITY #3

Comparing Cities With Box Plots

GUIDED PRACTICE: Holt page 697; 2 - 8 (EVENS)

INDEPENDENT PRACTICE: Holt page 697; 13, 15, 19, 25

Holt page 699; 45, 46, 47, 49, 50

General Tips

Always arrange the data in order from least to greatest first.

Always find the median second.

Remember to use a number line and scale your number line correctly for accuracy and proper distribution of your data.

The values plotted below the bottom whisker and above the top whisker, are considered outliers.You have three points: the first middle point (the median), and the middle points of the two halves (what I call the "sub-medians"). These three points divide the entire data set into quarters, called "quartiles". The top point of each quartile has a name, being a "Q" followed by the number of the quarter. So the top point of the first quarter of the data points is "Q1", and so forth. Note that Q1 is also the middle number for the first half of the list, Q2 is also the middle number for the whole list, Q3 is the middle number for the second half of the list, and Q4 is the largest value in the list.

Once you have these three points, Q1, Q2, and Q3, you have all you need in order to draw a simple box-and-whisker plot. Here's an example of how it works.

4.3,  5.1,  3.9,  4.5,  4.4,  4.9,  5.0,  4.7,  4.1,  4.6,  4.4,  4.3,  4.8,  4.4,  4.2,  4.5,  4.4

My first step is to order the set. This gives me:

3.9,  4.1,  4.2,  4.3,  4.3,  4.4,  4.4,  4.4,  4.4,  4.5,  4.5,  4.6,  4.7,  4.8,  4.9,  5.0,  5.1

The first number I need is the median of the entire set. Since there are seventeen values in this list, I need the ninth ...