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Let a, b ∈ R. Let the mean and the variance of 6 observations –3, 4, 7, –6, a, b be 2 and 23, respectively. The mean deviation about the mean of these 6 observations is :

1. 3 13
2. 3 16
3. 3 11
4. 3 14

Correct answer: 3 13

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