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About Bivariate Data — Class 8 IB

Create scatter plots, identify trends and correlations, and draw lines of best fit. This topic is part of the IB Class 8 mathematics syllabus (chapter: Unit 8). On this page you can practice 60 questions across three difficulty levels — 20 easy, 20 medium, and 20 hard — each with a visual step-by-step solution, plus a timed 35-question mastery test with a live leaderboard. Worked examples and sample questions from the topic are below.

Bivariate Data — solved examples for Class 8 IB

Example 1easy

What does a scatter plot show?
  1. A)The frequency of data
  2. B)The relationship between two variables
  3. C)The mean of a dataset
  4. D)The mode

Step-by-step solution

  1. A scatter plot displays pairs of data to show potential relationships between two variables.

Answer: The relationship between two variables

Example 2medium

Line of best fit: \(y = 5x + 40\). Predict the score for 8 hours of study.
  1. A)72
  2. B)75
  3. C)80
  4. D)85

Step-by-step solution

  1. Substitute:
    y=5(8)+40=80y = 5(8) + 40 = 80

Answer: 80

Example 3hard

Line of best fit: \(y = 2.5x + 15\). Actual value at x = 6 is 28. Find the residual.
  1. A)-2
  2. B)2
  3. C)-3
  4. D)3

Step-by-step solution

  1. Predicted: 2.5(6) + 15 = 30.
    Residual=28−30=−2\text{Residual} = 28 - 30 = -2

Answer: -2

Practice questions on Bivariate Data

  1. Q1.easy

    If points on a scatter plot trend upward from left to right, the correlation is:
    1. A)Negative
    2. B)Positive
    3. C)No correlation
    4. D)Perfect
    Show answer

    Answer: Positive

    Hint: Upward means both variables increase together.

  2. Q2.easy

    If points trend downward from left to right, the correlation is:
    1. A)Positive
    2. B)Negative
    3. C)Zero
    4. D)Undefined
    Show answer

    Answer: Negative

    Hint: Downward trend means one increases while the other decreases.

  3. Q3.easy

    What is the line of best fit?
    1. A)A line connecting all points
    2. B)A line that best represents the trend
    3. C)A vertical line
    4. D)A horizontal line
    Show answer

    Answer: A line that best represents the trend

    Hint: It doesn't have to pass through every point.

  4. Q4.medium

    Line of best fit: \(y = -2x + 100\). What does the slope mean?
    1. A)y increases by 2 per unit x
    2. B)y decreases by 2 per unit x
    3. C)Starting value is -2
    4. D)x has no effect
    Show answer

    Answer: y decreases by 2 per unit x

    Hint: Negative slope = decrease.

  5. Q5.medium

    Data: (1,2), (2,4), (3,5), (4,8), (5,9). Which point lies exactly on \(y = 2x\)?
    1. A)(1,2)
    2. B)(2,4)
    3. C)(3,5)
    4. D)(5,9)
    Show answer

    Answer: (1,2)

    Hint: Check each point in y = 2x.

  6. Q6.medium

    If \(r = -0.92\), describe the correlation.
    1. A)Strong positive
    2. B)Weak positive
    3. C)Strong negative
    4. D)No correlation
    Show answer

    Answer: Strong negative

    Hint: Close to -1 = strong negative.

  7. Q7.hard

    If \(r = 0.6\), interpret \(r^2 = 0.36\).
    1. A)36% of variation explained
    2. B)60% explained
    3. C)Strong relationship
    4. D)No relationship
    Show answer

    Answer: 36% of variation explained

    Hint: r² is a proportion.

  8. Q8.hard

    A student says ice cream causes sunburn because they're correlated. What error is this?
    1. A)Confusing correlation with causation
    2. B)Wrong formula
    3. C)Outlier effect
    4. D)Sampling error
    Show answer

    Answer: Confusing correlation with causation

    Hint: Correlation never proves causation.

  9. Q9.hard

    Mean point is (5, 12), slope = 3. The line of best fit passes through the mean. Find the equation.
    1. A)\(y = 3x - 3\)
    2. B)\(y = 3x + 12\)
    3. C)\(y = 3x - 5\)
    4. D)\(y = 5x + 3\)
    Show answer

    Answer: \(y = 3x - 3\)

    Hint: Use point-slope: y - 12 = 3(x - 5).

These are 9 of the 60 questions available for Bivariate Data. Start practicing above to unlock visual solutions, AI coaching, and the topic leaderboard — completely free.