GATE | GATE CS 2011 | Question 18

If the difference between expectation of the square of a random variable (E[X²]) and the square of the expectation of the random variable (E[X])² is denoted by R, then?
(A) R = 0
(B) R < 0
(C) R >= 0
(D) R > 0


Answer: (C)

Explanation: The difference between  (E[X²]) and (E[X])² is called variance of a random variable.  Variance measures how far a set of numbers is spread out. (A variance of zero indicates that all the values are identical.) A non-zero variance is always positive:

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