from random import *

def tirage() :
    p = 0.75
    nb_blanches = 0
    for i in range(3) :
        a = random()
        if a < p :
            nb_blanches = nb_blanches + 1
    return(nb_blanches)

def moyenne(n) :
    total = 0
    for i in range(n) :
            total = total + tirage()
    return ...