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

1 Plot and describe ★★★

A lemonade stand recorded the afternoon temperature (in °F) and the number of cups sold.

1. Which variable goes on the horizontal axis? Why?
2. Write the first and last ordered pairs.
3. Describe the association.

2 Name that association ★★★

Tell whether each pair of variables most likely has a positive association, a negative association, or no association.

1. Age of a car and its resale value.
2. Shoe size and score on a math quiz.
3. Hours of basketball practice and free throws made.
4. Distance walked and time spent walking at a steady pace.
5. Days absent and course grade.

3 Reading a scatter plot ★★★

Each point shows one used bike: age in years (horizontal) and price in hundreds of dollars (vertical).

1. Describe the association.
2. What is the price of the 4-year-old bike?
3. How many bikes cost more than 500 dollars?

4 Complete the totals ★★★

Forty students were asked how they get to school and whether they play soccer.

Find the four missing totals.

5 Spot the outlier ★★★

A student tracked the total pages read after each day.

One pair does not fit the pattern. Which one is the outlier? Explain.

6 Slope of a trend line ★★★

A trend line for the height of a sunflower (in centimeters) after \(x\) weeks passes through \((1, 15)\) and \((5, 35)\).

1. Find the slope.
2. Find the y-intercept.
3. Write the equation of the line.

7 Use the equation ★★★

A band director models the number of songs a group has memorized with \(y = 3x + 8\), where \(x\) is the number of weeks of rehearsal.

1. Predict the number of songs after 10 weeks.
2. After how many weeks does the model predict 50 songs?

8 Build the scatter plot ★★★

Eight students recorded their hours of sleep and the minutes they needed to solve a puzzle the next day.

1. Describe the association.
2. The line through \((6, 38)\) and \((9, 23)\) fits the data well. Find its equation.
3. Predict the time for a student who sleeps 8.5 hours.

9 Which line fits best? ★★★

The graph shows six points and three lines: A (violet), B (orange), and C (green).

1. Which line is the best line of fit?
2. Explain why each of the other two lines fits poorly.

10 Interpolate or extrapolate? ★★★

A seedling was measured each week for 10 weeks. The trend line is \(y = 4x + 12\), where \(y\) is height in centimeters and \(x\) is the week.

1. Predict the height in week 7.
2. Predict the height in week 30.
3. Which prediction is more trustworthy? Why?

11 Scooter rentals ★★★

A trend line for scooter rental data is \(y = 0.40x + 3\), where \(x\) is the ride time in minutes and \(y\) is the total cost in dollars.

1. Interpret the slope.
2. Interpret the y-intercept.
3. How many minutes can you ride with 10 dollars?

12 Honor roll and band ★★★

Eighty students were surveyed.

1. Complete the totals.
2. Find the percent of band students who are on the honor roll.
3. Find the percent of non-band students who are on the honor roll.
4. Is there an association?

13 Fill in from clues ★★★

A survey of 60 students gives these facts: 35 ride the bus and 25 walk; 24 students have a pet; 14 of the bus riders have a pet. Build and complete the two-way table.

14 Cats or dogs? ★★★

Sixty seventh graders and fifty eighth graders chose a favorite pet.

Is there an association between grade and favorite pet? Use relative frequencies.

15 The outlier effect ★★★

A pool sold season passes over seven weeks.

The first six weeks follow the line \(y = 4x + 8\).

1. Identify the outlier.
2. What does the line predict for week 7?
3. How far is the actual value from the prediction?
4. Suggest a real-world reason for this outlier.

16 Two clusters ★★★

Each point shows a player: weekly practice hours (horizontal) and free throw success percent (vertical).

1. Describe the clusters and the gap.
2. A line is drawn through all the points. Would it predict the success of a player who practices 5 hours? Explain.

17 Resale value ★★★

The trend line for the resale value (in dollars) of a phone \(x\) years after purchase passes through \((1, 640)\) and \((4, 400)\).

1. Find the equation.
2. Interpret the slope and the y-intercept.
3. When does the model predict a value of 0? Is that believable?

18 Fit your own line ★★★

Calories burned while jogging:

1. Describe the association.
2. Choose two points on a line that follows the trend and find its equation.
3. Predict the calories burned in 45 minutes.
4. Interpret the slope.

19 Association in a table ★★★

Two hundred students were asked whether they play a sport and whether they feel rested in the morning.

1. Find the percent of sport players who feel rested and the percent of non-players who feel rested.
2. Is there an association?
3. Of the students who feel rested, what percent play a sport?

20 Relative frequency table ★★★

Five hundred students were surveyed about transportation and school start time. The table shows percents of all 500 students.

1. How many students are in each of the four cells?
2. Among bus riders, what percent have an early start? Among walkers?
3. Is there an association?

21 Cause or coincidence? ★★★

A town finds a strong positive association between the daily temperature \(x\) (in °F) and ice cream sales \(y\) (in dollars): \(y = 1.5x - 60\).

1. At what temperature does the model predict 0 sales?
2. Interpret the slope.
3. A news headline says: "Buy less ice cream to cool the town." Explain the flaw.