Win Landsburg's Money (http://www.thebigquestions.com/2010/12/27/win-landsburgs-money/)

win.py

import random

nCouples = 1000000
nMales = nCouples/2
nFemales = nCouples/2
nSonlessCouples = nCouples

while nSonlessCouples > 0:
    for i in range(nSonlessCouples):
        if random.random() < 0.5:
            # it's a boy! stop trying
            nMales = nMales + 1
            nSonlessCouples = nSonlessCouples - 1
        else:
            # it's a girl! try again
            nFemales = nFemales + 1
    print 1. * nFemales / (nMales + nFemales)