Decently fast 'dice simulator' in Python for calculating chances and expected value for n throws

dice.py

import sys
import time
from collections import Counter
from random import randint

def chances(results):
    total = sum(results.values())
    return {k: v / total for k, v in results.items()}

def avg(chances):
    ret = 0.0
    for val, chance in chances.items():
        ret += val * chance
    return ret

def make_readable(chances):
    return {k: '{}%'.format(v * 100) for k, v in chances.items()}

def perform_throws(n):
    results = Counter()
    for i in range(n):
        results[randint(1, 6)] += 1
    cha = chances(results)
    print('End Result:\n Chances: %s\n Average: %f' % (
        make_readable(cha), avg(cha)))

def main():
    if len(sys.argv) < 2:
        print('Usage: dice.py <number of throws>')
        sys.exit(1)
    perform_throws(int(sys.argv[1]))

if __name__ == '__main__':
    main()