Exponentially increasing 50/50 chance.

exp.py

from random import randint
import time

start_time = time.time()
a = 0
b = 0

while a < 10:
	i = 0
	j = 0
	k = 0

	while i < 1:
		if randint(0, 10000) > randint(0, 10000):
			j += 1
		else:
			k += 1

		i += 1
	b += (time.time() - start_time)
	a += 1

print "1: %s" % (b/10)

start_time = time.time()
a = 0
b = 0

while a < 10:
	i = 0
	j = 0
	k = 0

	while i < 10:
		if randint(0, 10000) > randint(0, 10000):
			j += 1
		else:
			k += 1

		i += 1
	b += (time.time() - start_time)
	a += 1

print "10: %s" % (b/10)

start_time = time.time()
a = 0
b = 0

while a < 10:
	i = 0
	j = 0
	k = 0

	while i < 100:
		if randint(0, 10000) > randint(0, 10000):
			j += 1
		else:
			k += 1

		i += 1
	b += (time.time() - start_time)
	a += 1

print "100: %s" % (b/10)

start_time = time.time()
a = 0
b = 0

while a < 10:
	i = 0
	j = 0
	k = 0

	while i < 1000:
		if randint(0, 10000) > randint(0, 10000):
			j += 1
		else:
			k += 1

		i += 1
	b += (time.time() - start_time)
	a += 1

print "1000: %s" % (b/10)

start_time = time.time()
a = 0
b = 0

while a < 10:
	i = 0
	j = 0
	k = 0

	while i < 10000:
		if randint(0, 10000) > randint(0, 10000):
			j += 1
		else:
			k += 1

		i += 1
	b += (time.time() - start_time)
	a += 1

print "10000: %s" % (b/10)