The letters a, b, c, d, e, f have probabilities 1/2, 1/4, 1/8, 1/16, 1/32, 1/32 respectively. 1 / \ / \ 1/2 a(1/2) / \ / \ 1/4 b(1/4) / \ / \ 1/8 c(1/8) / \ / \ 1/16 d(1/16) / \ e f The average length = (1*1/2 + 2*1/4 + 3*1/8 + 4*1/16 + 5*1/32 + 5*1/32) = 1.9375