Lesson 4 Constructing Box Plots Warm up 3

Lesson 4 Constructing Box Plots

Warm up • 3, 4, 8, 12, 7, 5, 4, 12, 3, 9, 11, 4, 14, 8, 2, 10, 3, 10, 9, 7 • Find the minimum value, first quartile, median, third quartile and the maximum value.

Definition A box plot can be used to show the values in a data set are distributed. 5 values are needed: the minimum value, first quartile, median, third quartile and the maximum value.

Method • Example: the numbers of runs scored by a softball team in 20 games are given: • 3, 4, 8, 12, 7, 5, 4, 12, 3, 9, 11, 4, 14, 8, 2, 10, 3, 10, 9, 7

• Order the data from least to greatest. • Identify the 5 needed values. • the minimum value, first quartile, median, third quartile and the maximum value

• Draw a number line and plot a point above each of the 5 needed values. • Draw a box whose ends go through the 1 st and 3 rd quartiles, and draw a vertical line through the median. • Draw horizontal lines from the box to the min and max values.

Reflections • The lines that extend from the box in a box plot are sometimes called “whiskers”. • What part (lower, middle or upper) and about what percentage of the data does the box represent? • What part and about what percentage of the data does the whisker represent? • Which measures of spread can be determined from the box plot? • Calculate each measure.

Answers • Box: middle 50%; left whisker: lower 25%; right whisker: upper 25% • The range is the length of the entire box plot: • 14 – 2 = 12 • The IQR is the length of the box: 10 – 4 = 6

Assignment 4 • 1. Use the data to make a box plot. • 25, 28, 26, 18, 15, 28, 26, 16 • 2. 2, 3, 4, 1, 1, 3, 4, 2, 6, 2, 2, 3, 2