Introduction to Interquartile Range

Quartiles and IQR for grouped data

Lesson Objectives;

​

• ​Draw a cumulative frequency graph.

• ​Use the cumulative frequency graph to determine the Lower quartile, median and upper quartile.

• ​calculate the IQR for grouped data.

​Cumulative frequency graph and the IQR

​Watch the video on the next slide about drawing and cumulative frequency graph and using it to determine the quartiles and inter-quartile range, make some notes and respond to the proceeding quiz.

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Multiple Choice

What is the median length?

• 40.5 cm

• 30 cm

• 24.5 cm

• 32 cm

Multiple Choice

What is the Lower Quartile Length?

• 28 cm

• 30 cm

• 33 cm

• 20 cm

Multiple Choice

What is the Upper Quartile Length?

• 28 cm

• 30 cm

• 33 cm

• 20 cm

Multiple Choice

What is the Interquartile Range?

• 28 cm

• 12 cm

• 33 cm

• 5 cm

Multiple Choice

Approximately how many items were longer than 34 cm?

• None

• 8

• 7.5

• 7

Multiple Choice

Which is the correct cumulative frequency graph for the table given?

Multiple Choice

Fred carried out a survey of the time, in seconds, between one car and the next car on a road. His results are shown in the cumulative frequency graph. How many cars were in the survey?

• A. 40 cars

• B. 50 cars

• C. 60 cars

• D. 70 cars

• E. 80 cars

Multiple Choice

What is the interquartile range for the given graph?

• About 60

• About 7

• About 10

• Not enough information

Multiple Choice

Using the graph, which of the following is the estimation of the first quartile?

• 10

• 6

• 28

• 35

• 20

Poll

True or False: The median and quartiles can be estimated using a cumulative frequency graph.

• True

• False

Multiple Choice