Mean and Standard Deviation of a Normal Distribution | CFA Level 1 Exam Preparation

Mean and Standard Deviation of a Normal Distribution

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If 68% of the observations on a normal distribution fall between -20 and + 60, the mean and the standard deviation of the distribution are:

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A

Since the normal distribution is symmetrical about the mean, the mean is equal to (-20 + 60)/2 = 20. Further, for a normal distribution, 68% of the observations lie within one standard deviation of the mean. Therefore, the standard deviation equals 60-20 = 40.

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