Exercise 2 solution

import random
from fractions import Fraction

rng = random.Random(4)
families = 20000
hit = 0
for _ in range(families):
    affected_son = False
    for _ in range(3):
        if rng.choice("XY") == "Y" and rng.choice("Hh") == "h":
            affected_son = True
    hit += affected_son
exact = 1 - Fraction(3, 4) ** 3
print(hit, round(hit / families, 4))
print(exact, round(float(exact), 4))

Output:

11541 0.577
37/64 0.5781

Reading it: each child is a son with chance 1/2 and then affected with chance 1/2, so 1/4 per child. A family of three has no affected son with chance (3/4)^3 = 27/64, so at least one with 37/64, about 0.578. The simulation gave 11,541 of 20,000 (0.577), close to the exact value.