Working with the Variance of a Discrete Random Variable

By Consumer Dummies

Use the following formula for the variance of a discrete random variable X as needed to answer the following problems (round each answer to two decimal places):

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Sample questions

  1. If the variance of a discrete random variable X is 3, what is the standard deviation of X?

    Answer: 1.73

    The standard deviation is the square root of the variance, so if the variance of X is 3, the standard deviation of X is

    image1.jpg

    (rounded to two decimal places).

  2. If the standard deviation of X is 0.65, what is the variance of X?

    Answer: 0.42

    The variance is the square of the standard deviation, so if the standard deviation of X is 0.65, the variance of X is (0.65)2 = 0.4225. Rounded to two decimal places, the answer is 0.42.

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