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9th grade · Math · Unit 8 of 16

Data & Scatter Plots

Quartiles, box plots and correlation

What your child practices

Finding the median and quartiles of a data set, reading a box plot, telling positive, negative and no correlation apart, and using a line of best fit to make predictions. Correlation does not prove one thing causes another.

Texas Essential Knowledge and Skills (TEKS) teks student expectation: A.4(A); A.4(C) · correlation and linear models that fit data

How we explain it

Children can open this short lesson before they practice.

  1. A box plot shows the minimum, Q1, median, Q3 and maximum.
  2. A scatter plot shows how two variables relate.
  3. A line of best fit follows the trend.

Example: Data: 2, 4, 6, 8, 10. What is the median? Data is already in order. The middle value is 6. Answer: 6

Data & Scatter Plots in Texas

In the Texas Essential Knowledge and Skills (TEKS), this is unit 8 of 16 in 9th grade Math, after Solving Systems and before Two-Way Tables & Causation.

Gradelings describes a child's practice on this unit as Beginning, Approaching, Meeting or Exceeding (Four practice steps). That reflects practice, not a report-card mark: the teacher decides the mark.

Source: Texas Education Agency (TEA)

Sample questions

A taste of this unit. In the app, questions change every time and get easier or harder to match your child.

  1. Question 1

    Eight students recorded the minutes they read last night: 28, 44, 46, 58, 38, 60, 52, 34. What is the first quartile, Q1?

    answer box

  2. Question 2

    As the number of hours of study goes up, test marks tend to go up too. What kind of correlation is this?

    • Positive correlation
    • A perfect fraction
    • No correlation
    • Negative correlation

  3. Question 3

    A line of best fit for hours of practice (x) and score (y) is y = 4x + 16. What score does the model predict after 7 hours?

    answer box

  4. Question 4

    Eight students recorded the minutes they read last night: 23, 25, 15, 17, 29, 11, 21, 19. What is the interquartile range (Q3 − Q1)?

    answer box

  5. Question 5

    Which type of graph shows the relationship between two numerical variables?

    • A pictograph
    • A bar graph of one variable
    • A scatter plot
    • A circle graph

  6. Question 6

    On a box plot, the median line is much closer to Q1 than to Q3. What does this tell you?

    • There are no values below the median
    • The mean must equal the median
    • The data between the median and Q3 is more spread out than the data between Q1 and the median
    • The data between Q1 and the median is more spread out

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