Scatter Plots & Best Fit · Grades 8–9
Scatter Plot and Line of Best Fit Worksheets
Read the correlation, spot the outlier, count points past a line, and predict with a line of best fit, on scatter plots built from real-looking data: study time, temperature, car prices.
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What it is
A scatter plot shows pairs of data as points. If the points rise from left to right, the correlation is positive; if they fall, negative; if there is no pattern, there is no correlation. Points close to a line show a strong correlation; spread-out points, a weak one. A line of best fit runs through the middle of the points and can be used to predict.
Why it matters
Scatter plots are how anyone checks whether two things are related, from sales and weather to sleep and grades. A line of best fit turns that pattern into a prediction.
How to do it
- Correlation: as x increases, does y tend to increase (positive), decrease (negative) or neither (none)?
- Strength: points close to a straight line are strong; loosely scattered points are weak.
- An outlier is a point far from the pattern of the others.
- To predict, go up from the x-value to the line of best fit, then across to read y.
- Equation of a best-fit line: slope = change in y ÷ change in x between two points on it; the y-intercept is where it crosses the y-axis. Predicting inside the data is interpolation; beyond it, extrapolation.
Examples by level
Use each scatter plot, or the equation given, to answer the question.
- BeginnerDescribe the correlation (strong or weak, positive or negative).AnswerStrong negative
- IntermediateUse the line of best fit to predict the battery left after 7 h of use.AnswerAbout 49%
- AdvancedUse the line of best fit to predict the ice creams sold at 28°C.AnswerAbout 40
Examples are generated by the same engine as the worksheets, so they're always mathematically correct. Built to avoid repeats, not reshuffle the same handful of questions.
Common mistakes
- Calling a weak trend 'no correlation' because the points don't sit on a line.
- Reading a prediction from the nearest dot instead of from the line.
- Trusting a prediction far outside the data (extrapolation).
Tips
- A line of best fit has about as many points above it as below.
- Correlation shows a relationship, not that one thing causes the other.
For parents
Ask what happens to one quantity as the other goes up: that's the direction of the correlation.
For teachers
Have students sketch their own best-fit line before using the drawn one, then compare predictions.
Key vocabulary
- correlation
- how two quantities change together: positive, negative or none
- outlier
- a data point far from the others
- line of best fit
- a straight line that best shows the trend of the points
Frequently asked questions
- What is a line of best fit?
- A straight line drawn through the middle of the points, with about as many above it as below, to show the trend.
- What's the difference between interpolation and extrapolation?
- Interpolation predicts inside the range of the data; extrapolation goes beyond it and is less reliable.
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