Var(X) = E[X2] – E[X]2 = 12 . P[X=1] – p2

= p – p2 = p(1-p) Exercise!

var(∑ixi)=∑ivar(xi) for independent xi

pe = p if e = 1pe = 1 if e = 0

Result: we have transformed a single categorical variable taking one of m values ai into an m-dimensional numeric variable taking value 1 in the ith column and 0 elsewhere

Bins -> Categorical attributes {a1, a2, a3, a4}

One categorial variable Ai for each possible attribute value ai

= n! / (n1! n2!...nm!) = #ways of choosing m subsets of sizes n1, n2,…,nm