Variance from Coin Tossing

Let $$X$$ be the random variable denoting the number of heads out of 100 independent, fair coin tosses. What is the variance of $$X$$?

Details and assumptions

The variance of a random variable measures the extent to which values are spread out. It can be calculated as $$\mbox{Var}(X) = \sum (X- \bar{X})^2 f(x)$$.

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