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Grade 7 - Mathematics
10.2 Box-and-Whisker Plot

  • Central tendency describes the middle or a typical value of the data set and is measured using the mean, median, and mode.
  • Variability describes how spread out the data is.
  • Quartiles divide a data set into four equal parts. The third quartile minus the first quartile is the range for the middle half of the data.
  • A box-and-whisker plot shows the distribution of data. The middle half of the data is represented by a box with a vertical line at the median. the lower first and upper fourth are represented by whiskers that extend to the smallest and largest values.
Example:
Draw a box-and-whisker plot for the table below, that summarizes a veterinaian's record for kitten litters born in a given year.

Litter Size2 3 4 56
Number of Litters1 6 8 111

  1. Order the data and find the smallest value, first quartile, median, third quartile and largest value.
    2 3 3 3 3 3 3 4 4 4 4 4 4 4 4 5 5 5 5 5 5 5 5 5 5 5 6

    Lower half
    Upper half
    2 3 3 3 3 3 3 4 4 4 4 4 4
    4
    4 5 5 5 5 5 5 5 5 5 5 5 6
    First quartileSecond quartile Third quartile
    median of lower half:3Median:4 median of upper half:5

    smallest value: 2
    first quartile: 3
    median: 4
    third quartile: 5
    largest value: 6

  2. Draw a number line and plot above each value from step 1

  3. Draw the box and whiskers.

Directions: Answer the following questions. Also write at least 5 examples of your own.
Q 1: Find the third quartile of the following data:
85,92,78,88,90,88,89
Answer:

Question 2: This question is available to subscribers only!


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