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The mean square deviation of n observations about a point c is (1/n) * sum (xi - c)². If the mean square deviations about -2 and about 2 are 18 and 10 respectively, find the standard deviation of the data.

1. 3
2. 2
3. 1
4. None of these

Correct answer: 3

Solution

Using MSD(c) = sigma² + (xbar - c)²: subtracting gives xbar = 1, then sigma² = 9, so sigma = 3.

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