Pre-View of a box and whisker plot

1. What is the scale and interval of the
number line below the plot?
2. Are you able to tell how many parts the
data set is divided into?
3. What do you think the far right and far left
points represent (at the end of the
4. What do you think the line inside the box
 Where do you think the following labels should go on
our box and whisker plot?
 Upper extreme, Lower extreme, second (lower) quartile,
third (upper) quartile, interquartile range, and median.
Uses a number line to show the distribution of a set of data. It
divides a set of data into four parts using the median and
quartiles. A box is drawn around the quartile values, and
whiskers extend from each quartile to the minimum and
maximum values that are not outliers.
 Quartiles
 The median is the middle quartile
 The median of the lower half of the data is the lower
 The median of the upper half of the data is the upper
 The lower extreme forms the lower whisker.
 The upper extreme forms the upper whisker.
 Interquartile Range (IQR) is the difference between
the upper quartile and the lower quartile
 Step 1: Find the median, lower quartile, and
upper quartile.
 Step 2: Find the interquartile range.
 Step 3: Multiply the interquartile range by
 Step 4: Subtract the value from the lower
quartile and add the value to the
upper quartile.
 Find any outliers in the
data set.
Animal Speeds
Speed (mph)
Glencoe Pre-Algebra (2012) pg. 793
 Step 1: median - 30
lower quartile - 15
upper quartile - 35
 Step 2: interquartile range
35 – 15 = 20
 Step 3: IQR x 1.5
20 x 1.5 = 30
 Step 4: lower quartile – 30
15 – 30 = -15
upper quartile + 30
35 + 30 = 65
70 is an outlier
 1. Organize the data from smallest to largest.
 2. Identify the lower extreme, lower quartile, median,
 3.
 4.
 5.
 6.
 7.
upper quartile, upper extreme.
Find the interquartile range.
Identify any outliers, use an asterisk(*) to indicate
an outlier. It is not connected to a whisker.
Draw the number line, mark the scale, and label the
Draw the box plot.
Give the box plot a title.
 Write 3-5 sentences summarizing the data displayed.
The shortest hair measured was 9 cm.
The lower quartile is 13 cm.
The median is 25 cm.
The upper quartile is 33 cm.
The longest hair measured was 42 cm.
The range is 42 cm – 9 cm or 33 cm.
The interquartile range is 33 cm -13 cm = 20 cm
The middle half of the data lies between 33 and 13. So the
middle half of the girls measured had hair between 33cm
and 13 cm. This is more variability in the lower half of the
data indicating that more girls had hair lower than 25 cm
than had hair longer than 25 cm.
 The box plot provides a summary of the data. It does
not show the number of observations (so you can’t find
the mean) nor does it indicate if a particular value was
especially common (so you can’t find the mode).
 1. The range is always, sometimes, or never affected by
outliers. Justify your reasoning.
 2. True or false. The interquartile range is affected by
outliers of the data set. Explain your reasoning.
 3. It is always, sometimes, or never possible for the
mean, median, and mode to be equal? Justify your
 4. Can a data set have more than one median?
Glencoe Pre-Algebra (2012) pg. 778 and 796

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