Maths Literacy Matric Revision: Box-and-whisker plots

CAPS Mathematical Literacy Grade 12: Box-and-Whisker Plots Revision Notes


Box-and-whisker plots are a type of graphical representation used in statistics to display the distribution of a dataset. They are particularly useful for identifying the spread of the data, detecting outliers, and comparing different sets of data.


Understanding box-and-whisker plots is important for interpreting data distributions, which is a critical skill in data analysis. They help in visualizing the five-number summary: minimum, first quartile (Q1), median (Q2), third quartile (Q3), and maximum. This information is crucial in many real-world applications such as comparing test scores, analyzing financial data, and more.

Key Points

  1. Components of a Box-and-Whisker Plot:

    • Box: Represents the interquartile range (IQR), which contains 50% of the data.
    • Whiskers: Extend from the box to the minimum and maximum values within 1.5 times the IQR from Q1 and Q3.
    • Median (Q2): The middle value of the data set, represented by a line inside the box.
    • Outliers: Data points outside the whiskers, often shown as dots or asterisks.
  2. Five-Number Summary:

    • Minimum: The smallest data point.
    • Q1 (First Quartile): The median of the first half of the dataset.
    • Median (Q2): The middle value of the dataset.
    • Q3 (Third Quartile): The median of the second half of the dataset.
    • Maximum: The largest data point.
  3. Drawing a Box-and-Whisker Plot:

    • Order the data from least to greatest.
    • Identify the five-number summary.
    • Draw a number line including the range of the dataset.
    • Draw a box from Q1 to Q3.
    • Mark the median inside the box.
    • Extend whiskers from the box to the minimum and maximum values.
    • Plot any outliers.

Real-World Applications

Example Problem:
Given the dataset: 21, 23, 24, 25, 29, 33, 49, draw a box-and-whisker plot.

1. Order the data: 21, 23, 24, 25, 29, 33, 49.
2. Five-number summary:
– Minimum: 21
– Q1: 23
– Median (Q2): 25
– Q3: 33
– Maximum: 49
3. Draw the plot:
– Draw a box from 23 (Q1) to 33 (Q3).
– Draw a line at 25 (Median).
– Extend whiskers from 21 (Minimum) to 49 (Maximum).

Common Misconceptions and Errors

  • Confusing quartiles: Quartiles divide the data into four equal parts, not the dataset into four equal data points.
  • Incorrectly identifying outliers: Outliers are points outside 1.5 times the IQR, not just any points far from the mean.

Practice and Review

Practice Questions:
1. Given the dataset [12, 15, 14, 10, 21, 20, 18], draw a box-and-whisker plot.
2. The following are examination results out of 50: [35, 40, 46, 42, 38, 49, 50, 32]. Identify the outliers if any.

Detailed step-by-step solutions and explanations can solidify understanding.

Examination Tips:
– Keywords: “five-number summary,” “interquartile range (IQR),” “outliers”
– Efficient Time Management: Start with drawing the number line and identifying the five-number summary.

Connections and Extensions

Interdisciplinary Links:
Economics: Use box-and-whisker plots to compare economic indicators like income distributions.
Biology: Analyze the spread of biological data such as heights or weights in a population.

Encourage exploring connections to understand the versatility and utility of box-and-whisker plots across different fields.

Summary and Quick Review

  • Box-and-whisker plots visualize data distribution, highlighting the spread and outliers.
  • Five-number summary: Minimum, Q1, Median, Q3, Maximum.
  • Useful for comparing multiple data sets and understanding overall data distribution.

Additional Resources

By mastering box-and-whisker plots, students will be better equipped to analyze and interpret data effectively in various academic and real-world scenarios.

For further reading and practice, refer to the CAPS Mathematical Literacy Grade 12 study guide【4:1†source】【4:5†source】.

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