8th grade statistics and probability

Question 1

Data was collected for x from 1 to 8, and the line of best fit is y = 4x + 6. Jamal uses it to predict y when x = 30. Why should Jamal be careful?

• A. Lines of best fit can never be used
• B. The line has a positive slope
• C. x is far outside the data range, so the trend may not continue
• D. The answer will be a decimal

Question 2

Year 7 — cats 9, dogs 5; Year 8 — cats 16, dogs 10. A Year 7 student is picked at random. What is the probability they prefer cats? Give a fraction in simplest form.

Answer (as a fraction)

Question 3

A line of best fit is y = 3x + 3. For which x does it predict y = 33?

Answer 

Question 4

For plants, the line of best fit of height in cm (y) against age in weeks (x) is y = 3x + 27. What does 3 mean?

• A. Plants grow about 3 cm per week
• B. Plants grow 27 cm per week
• C. Plants are 3 cm tall at the start
• D. Plants grow for 3 weeks

Question 5

The line of best fit for hours studied (x) and test score (y) is y = 3x + 6. Predict the score for 4 hours of study.

Answer 

Question 6

What kind of association does the scatter plot show?

• A. Positive association
• B. Negative association
• C. No association

Question 7

A two-way table: Year 7 — cats 5, dogs 14; Year 8 — cats 18, dogs 9. How many students are in the table altogether?

Answer 

Question 8

50 students in Club A and 60 students in Club B were asked if they recycle at home. 15 in Club A and 24 in Club B said yes. What percentage of Club A recycle at home?

Answer 

Question 9

Does this scatter plot show a linear or a nonlinear association?

• A. Linear
• B. Nonlinear

Question 10

What association would you expect between: Height of a tree and the length of its shadow at noon?

• A. Positive
• B. Negative
• C. None

Question 11

Year 9 survey. Have a pet: 9 with a phone, 19 without. No pet: 21 with a phone, 19 without. Of the students WITH a phone, what fraction have a pet? Give a fraction in simplest form.

Answer (as a fraction)

Question 12

The line of best fit for the cost of a taxi ride (y, in currency units) against distance (x, in km) is y = 3x + 27. What does 27 represent?

• A. The longest possible trip
• B. The cost per km
• C. The cost of a 27 km trip
• D. The predicted cost for a 0 km trip (the starting charge)

Question 13

Nia plotted two measurements for 8 plants in a scatter graph. What type of correlation does it show?

• A. Positive
• B. Negative
• C. No correlation

Question 14

Which point is an outlier in this scatter plot?

• A. (1, 4)
• B. (7, 16)
• C. (3, 5)
• D. (5, 7)

Question 15

The line of best fit for test score (y) against hours of practice (x) is y = 3x + 49. Predict the score after 3 hours.

Answer 

Question 16

In Class X, 24 of 40 students bike to school. In Class Y, 16 of 40 students bike to school. Which class has the higher proportion of cyclists?

• A. X
• B. Y
• C. The same