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Let a 1 , a 2 , ... a 10 be 10 observations such that ∑ = = 10 1 k k 50 a and ∑ < ∀ j k j k a . a = 1100. Then the standard of deviation of a 1 , a 2 , ..., a 10 is equal to:

1. 5
2. 115
3. 10
4. 5

Correct answer: 5

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