4 a 0: $(1/2)^4 * 2 = 1/8 = 2/16$
4 a 1: $(1/2)^4 * 4* (1/2)*2 = 1/4= 4/16$
4 a 2: $(1/2)^5 * 10* (1/2)*2 = 5/16$
4 a 3: $(1/2)^6 * 20* (1/2)*2 = 5/16$
Totale: $16/16$ e meno male. Ma ci basta calcolare 4 a 2: $(1/2)^5 * 10* (1/2)*2 = 5/16$ come ho fatto prima.