Let a1,a2,...,a10 be 10 observations such that ∑k=110ak=50 and ∑∀k<jak·aj=1100. Then the standard deviation of a1,a2,…,a10 is equal to :

Question

Let

a_{1}, a_{2}, . . ., a_{10}

10

observations such that

\sum_{k = 1}^{10} a_{k} = 50

and

\sum_{\forall k < j} a_{k} \cdot a_{j} = 1100

. Then the standard deviation of

a_{1}, a_{2}, \dots, a_{10}

is equal to :

5

\sqrt{5}

10

\sqrt{115}

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