answer - 3.9
let X be random variable denoting length of word drawn. We have to calculate E(X)
there are 4 words of length 3, 2 words of length 4 and 3 words of length 5
probability of choosing a word of length 3 = 4/9
probability of choosing a word of length 4 = 2/9
probability of choosing a word of length 5 = 3/9
E(X) = (4/9)x3 + (2/9)x4 + (3/9)x5 = 3.9