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9th grade · Math · Unit 9 of 17

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.

Maine Learning Results learning standard: HSS.ID.A.1; HSS.ID.B.6; HSS.ID.C.7 · box plots, scatter plots and the strength of an association

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 Maine

In the Maine Learning Results, this is unit 9 of 17 in 9th grade Math, after Lines & Intersections and before Function Notation.

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: Maine Department of Education

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

    As the outdoor temperature falls in winter, the heating bill tends to rise. What kind of correlation is this?

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

  2. Question 2

    Eight students recorded the minutes they read last night: 33, 37, 45, 51, 29, 23, 19, 39. What is the median?

    answer box

  3. Question 3

    Eight students recorded the minutes they read last night: 32, 42, 58, 52, 50, 36, 44, 38. What is the interquartile range (Q3 − Q1)?

    answer box

  4. Question 4

    Eight students recorded the minutes they read last night: 42, 40, 32, 18, 26, 20, 28, 38. What is the first quartile, Q1?

    answer box

  5. Question 5

    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 data between Q1 and the median is more spread out
    • 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

  6. Question 6

    A line of best fit is used to…

    • Prove one variable causes the other
    • Join every point exactly
    • Describe the trend and predict values
    • Make the data larger

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