Scatter Plots and Two-Way Tables: math test, Grade 8 – download the PDF

1 Reading a scatter plot / 4 pts

Each point shows a puppy: months of training (horizontal) and number of commands learned (vertical).

1. Describe the overall association. (1 pt)
2. Identify the outlier and suggest a reason for it. (1 pt)
3. How many commands does the puppy trained for 4 months know? (1 pt)
4. How many puppies know at least 7 commands? (1 pt)

2 Equation of a trend line / 4 pts

A trend line for the money saved (in dollars) after \(x\) weeks passes through \((2, 14)\) and \((8, 32)\).

1. Find the slope. (1 pt)
2. Find the equation of the line. (1 pt)
3. Interpret the slope. (1 pt)
4. Interpret the y-intercept. (1 pt)

3 Making predictions / 3 pts

A model for the length of a weekly run is \(y = 1.2x + 3\), where \(x\) is the week of training and \(y\) is the distance in miles.

1. Predict the distance in week 10. (1 pt)
2. In which week does the model predict a 21-mile run? (1 pt)
3. Would the model be reasonable for week 60? Explain. (1 pt)

4 Breakfast and lateness / 4 pts

One hundred fifty students were asked whether they eat breakfast and whether they were late to first class.

1. Complete the totals. (1 pt)
2. Find the percent late among breakfast eaters and among students who skip breakfast. (1.5 pts)
3. Is there an association? Explain. (1.5 pts)

5 True or false? / 3 pts

Say whether each statement is true or false, and justify.

1. A line of best fit must pass through the origin. (1 pt)
2. A strong association proves that one variable causes the other. (1 pt)
3. An outlier can change the position of a line of best fit. (1 pt)

6 Residual check / 2 pts

A line \(y = 2x + 1\) models the first six points of a data set. The seventh point is \((7, 5)\).

1. What does the line predict for \(x = 7\), and how far off is the actual point? (1 pt)
2. What would happen to the line if this point were included? (1 pt)