Variance from Coin Tossing

Probability Level 3

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 $\mbox{Var}(X) = \sum (X- \bar{X})^2 f(x)$ .