Grade 9 · Math · Unit 7 of 7
Statistics in Society
Samples, bias and misleading graphs
What your child practises
Telling a population from a sample, spotting bias in who is asked and how, predicting from a sample, noticing misleading graphs, and why correlation is not causation.
Saskatchewan Curriculum outcome: SP9.1, SP9.2 · collecting and analyzing data, and what can bias it
Sample questions
A taste of this unit. In the app, questions change every time and get easier or harder to match your child.
Question 1
A school has 200 students. A survey asks 10 of them. What fraction of the students were surveyed? Type it in lowest terms.
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1/20
Hint: Fraction = 10/200, which is 1/20 in lowest terms.
Question 2
In a random sample of 50 students, 20 said they walk to school. Based on this sample, about how many of 800 students walk?
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320
Hint: The sample proportion is 20/50. Multiply by the population: 20/50 × 800 = 320.
Question 3
Four students report hours of sleep: 7, 8, 9, 8. What is the mean?
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8
Hint: Add them: 32. Divide by 4: 8.
Question 4
A poll is conducted by phoning only landlines on weekday mornings. Who might be missing?
- people who answer the phone
- nobody
- only teachers
- people who work during the day or only use cell phones
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people who work during the day or only use cell phones
Hint: Who is left out of the sample can bias the result.
Question 5
Which sample is most likely to represent all students at a school?
- 50 students who volunteered online
- the 50 students on the basketball team
- 50 students chosen at random from the school list
- 50 students at the lunch table nearest the gym
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50 students chosen at random from the school list
Hint: A random sample gives every student an equal chance to be chosen.
Question 6
A sample is…
- the mean
- a smaller group chosen to represent the population
- a type of graph
- the whole population
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a smaller group chosen to represent the population
Hint: Surveying everyone is often impossible, so we study a sample.