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Cogito

Grade 7 Math · Chapter 9 · Lesson 2

Practice Worksheet

Samples and What They Tell You

Asking some to learn about all.

10 problems · about 18 minutes · 7.SP.A.1, 7.SP.A.2

NameDate

Figure — use these to answer the problems

Scaling a sample up to a population is a ratio, so it multiplies.
A ratio table for 5 to 2
In the sampleIn the population
52
104
156
208
In the sampleIn the population0052104156208
Sampled5
Preferred blue2
Scale it up by4
Figure 1

Warm-Up Review

From earlier lessons. Loosen up before the new work.

2 problems

  1. From “Probability as a Number”

    A fair die. Out of 6, how many outcomes are less than 3?

    Answer

  2. From “When Three Measurements Fix a Triangle”

    Can sides 4, 4 and 9 make a triangle? 1 for yes, 0 for no.

    Answer

Warm Up

Straightforward practice. Get the method working first.

4 problems

  1. 9 of 30 sampled. In 300, about how many?

    Answer

  2. What makes a sample useful?

    • It represents the whole population fairly.
    • It is as large as possible.

  3. 8 of 40 sampled. In 200, about how many?

    Answer

  4. 6 of 25 sampled. In 100, about how many?

    Answer

Build It Up

The same ideas with more to keep track of.

2 problems

  1. 30 of 60 sampled. In 400, about how many?

    Answer

  2. Should a sample favour one group?

    • No.
    • Yes.

Stretch Yourself

Mixed problems. Work out what kind of question it is before you start.

2 problems

  1. The Survey

    15 of 50 sampled prefer tea. In 500 people, about how many would prefer tea?

    Answerpeople

  2. The Bad Sample

    Asking only people in a library about reading. Is that representative?

    • No. Library visitors read more than most.
    • Yes.