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Plot a drapht with the above grouped data. Using the frequency and class midpoint. Explain skewness distribution

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Step-by-step solution

6 steps

Here's how to plot the graph and understand skewness:

Part a· 6 steps

Plot a graph with the above grouped data (frequency and class midpoint)

  1. List the data points (class midpoint, frequency) from the table

    • $(34.5, 1)$
    • $(45.5, 3)$
    • $(54.5, 4)$
    • $(64.5, 7)$
    • $(74.5, 5)$
    • $(84.5, 4)$
    • $(94.5, 2)$
  2. Draw a horizontal axis (x-axis) and label it "Class Midpoint".

    Mark the midpoints at equal intervals.

  3. Draw a vertical axis (y-axis) and label it "Frequency".

    Scale it from 0 to at least 7 (the maximum frequency).

  4. Plot each data point on the graph.

    For example, place a dot at the intersection of 34.5 on the x-axis and 1 on the y-axis.

  5. Connect the plotted points with straight lines.

  6. To complete the frequency polygon, extend the line to the midpoint of the class before the first class (which would be 24.5 with frequency 0) and to the midpoint of the class after the last class (which would be 104.5 with frequency 0).

Part b

Explain skewness distribution

Skewness is a measure of the asymmetry of the probability distribution of a real-valued random variable about its mean. A distribution is skewed if it is not symmetrical on both sides of its central peak.

  • Positive Skew (Right Skew): The tail of the distribution is longer on the right side. This means there are more extreme values on the higher end. In a positively skewed distribution, typically the mean is greater than the median, which is greater than the mode (Mean>Median>Mode\text{Mean} > \text{Median} > \text{Mode}).
  • Negative Skew (Left Skew): The tail of the distribution is longer on the left side. This means there are more extreme values on the lower end. In a negatively skewed distribution, typically the mean is less than the median, which is less than the mode (Mean<Median<Mode\text{Mean} < \text{Median} < \text{Mode}).
  • Symmetrical Distribution: The distribution is balanced on both sides of its central peak. For a perfectly symmetrical distribution, the mean, median, and mode are all equal (Mean=Median=Mode\text{Mean} = \text{Median} = \text{Mode}).

For the given data:
The frequencies are 1,3,4,7,5,4,21, 3, 4, 7, 5, 4, 2. The mode is at 64.5 (frequency 7).
The distribution has a longer tail towards the higher values (right side) compared to the lower values.

  • Mean ≈66.92\approx 66.92
  • Median ≈66.64\approx 66.64
  • Mode =64.5= 64.5 Since Mean>Median>Mode\text{Mean} > \text{Median} > \text{Mode}, the distribution is positively skewed (or right-skewed).
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