1A.2 Dot Plots and

Measures of Dispersion

Vocabulary

Dot PlotA graph that shows the frequency of values in a data set

Measure of DispersionA measure that describes the spread of a data set

To Create a Dot Plot: 1) Find the minimum and maximum value in your data set.

2) Draw a number line going from the minimum value to the maximum value.

3) Place a dot above the number on the number line for each number in your data set. If there is already a dot above the number, add an additional dot above the existing one.

When you are finished there should be a dot on the graph for each piece of data in the data set.

Draw a dot plot of the data and then find the mean, median and mode of the data.

Bag 1 2 3 4 5 6 7 8 9

Strawberries 10 13 11 15 8 14 7 11 12

Find the mean, median, mode and range for the dot plot

Directions: Make a double dot plot for the data below.

Points in ten baseball games

Hall HS: 4, 4, 6, 6, 8, 3, 3, 2, 1, 1

Conard HS: 2, 4, 8, 9, 5, 5, 1, 1, 2, 0

1.) 2.)

After the first week, the 25-year-old is voted off Show A and the 48-year-old is voted off Show B. How does this affect the mean and range of the remaining contestants on each show?

Standard DeviationThe standard deviation of a data set is a measure of how much a typical value in the data set differs from the mean.

standard deviation n

xxxxxx n22

22

1 )()()(

• where n is the number of values in the data set• the symbol represents the mean. It is read as “x-

bar”

20 25

29 25

19 25

22 25

25 25

27 25

27 25

29 25

30 25

20 25

21 25

31 25

x xx 2)( xx x

Find the standard deviation of the ages for Show B in Example 1. Interpret your results.

x xx 2)( xx x

You are the general manager of an NBA team. You are 35 games into the season and you are planning to sign a new player. You are choosing between player X and player Y. The points they have scored in every game so far are shown in the dot plots below. If you could sign player Y for 4 million dollars, how much more would you be willing to pay player X? Why? Justify your answer with calculations, using the ideas of center and spread.

Player X – Points per game

Player Y – Points per game