Lesson 9

What Makes a Good Sample?

Let’s see what makes a good sample.

Problem 1

Suppose 45% of all the students at Andre’s school brought in a can of food to contribute to a canned food drive. Andre picks a representative sample of 25 students from the school and determines the sample’s percentage.

He expects the percentage for this sample will be 45%. Do you agree? Explain your reasoning.

Problem 2

This is a dot plot of the scores on a video game for a population of 50 teenagers.

A dot plot for “score on a video game.” The numbers 40 through 200, in increments of 10, are indicated. 

The three dot plots together are the scores of teenagers in three samples from this population. Which of the three samples is most representative of the population? Explain how you know.

Three dot plots for “score on a video game” are labeled “sample 1,” “sample 2,” and “sample 3.” The numbers 40 through 200, in increments of 10, are indicated

Problem 3

This is a dot plot of the number of text messages sent one day for a sample of the students at a local high school. The sample consisted of 30 students and was selected to be representative of the population.

A dot plot for “number of text messages sent.” The numbers 0 through 90, in increments of 5, are indicated.

  1. What do the six values of 0 in the dot plot represent?

  2. Since this sample is representative of the population, describe what you think a dot plot for the entire population might look like.

Problem 4

A doctor suspects you might have a certain strain of flu and wants to test your blood for the presence of markers for this strain of virus. Why would it be good for the doctor to take a sample of your blood rather than use the population?

(From Unit 8, Lesson 8.)