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If the data x 1 , x 2 , …… x 10 is such that the mean of first four of these is 11, the mean of the remaining six is 16 and the sum of squares of all of these is 2,000 ; then the standard deviation of this data is :

1. 2
2. 2
3. 2 2
4. 4

Correct answer: 2

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