To graph and interpret Box-and-Whisker Plots

Do Now: Order the set of numbers from least to greatest, then find the median.

The Median

3. Find the lower and upper medians or quartiles. These are the middle numbers on each side of the median. What are they?

Step 3 – Upper & Lower Quartiles

Now you are ready to construct the actual box & whisker graph. First you will need to draw an ordinary number line that extends far enough in both directions to include all the numbers in your data:

Step 4 – Draw a Number Line

Locate the main median 12 using a vertical line just above your number line:

Step 5 – Draw the Parts

Locate the lower median 8.5 and the upper median 14 with similar vertical lines:

Step 5 – Draw the Parts

Next, draw a box using the lower and upper median lines as endpoints:

Step 5 – Draw the Parts

Finally, the whiskers extend out to the data's smallest number 5 and largest number 20:

Step 5 – Draw the Parts

Step 6 - Label the Parts of a Box-and-Whisker Plot

Q3Q1

Name the parts of a Box-and-Whisker Plot

Median Upper Quartile

Lower QuartileMin Max

Interquartile RangeThe interquartile range is the difference between the upper quartile and the lower quartile.

14 – 8.5 =5.5

Upper Quartile = 10

Q3

Lower Quartile = 4

Q1

Median = 8

Q2

3, 4, 4, 6, 8, 8, 8, 9, 10, 10, 15,

Find the median, quartiles and inter-quartile range.

6, 3, 9, 8, 4, 10, 8, 4, 15, 8, 10 Order the data

Inter-Quartile Range = 10 - 4 = 6

Construct a box plot for this data.

Applications of Box Plots A box-and-whisker plot helps to

show how varied, or spread out, the data are.

Box plots are useful for comparing two or more sets of data.

130 140 150 160 170 180 190

Boys

Girlscm

Box and Whisker Diagrams.

Box Plots

Emma recorded the heights in cm of students in the same class and constructed a box plot from the data. The box plots for both boys and girls are shown below.

Interpreting a Box-and-Whisker Plot The large box (IQR) represents about half of the

data. Each small box represents about one quarter of the data.

Each whisker represents about one quarter of the data

Activity 1.3 Construct a box-and-whisker plot for the following

data:Math test scores 80, 75, 90, 95, 65, 65, 80, 85, 70, 100, 50

Additional Practice http://www.warrick.k12.in.us/school

s/castlesouth/docs/Math/Math7Book/Math%207%20Ch%203.4%20p123.pdf