The Tuesday Birthday Problem (alexbellos.com)

For further discussion by Stanford's Keith Devlin, see http://www.maa.org/devlin/devlin_04_10.html

Author John Allen Paulos nicely clarifies the intuition behind the solution here: http://twitter.com/JohnAllenPaulos/status/11699672607

Python 2.6.4 (r264:75821M, Oct 27 2009, 19:48:32)

  >>> from itertools import product
  >>> twokids = product('B G'.split(), 'M Tu W Th Fr St Sn'.split(), repeat=2)
  >>> boytues = [t for t in twokids if t[:2]==('B', 'Tu') or t[2:]==('B', 'Tu')]
  >>> twoboys = [t for t in boytues if t[0] == t[2] == 'B']
  >>> len(twoboys)
  13
  >>> len(boytues)
  27

I (really) am a boy born on a Tuesday. And I have one sibling, a sister. Anyhow, this looks the same as this problem:

Given a standard deck of cards.

(a) "I have two cards and one is an ace. What is the probability the second card is also an ace?"

(b) "I have two cards and one is the ace of Hearts. What is the probability the second card is also an ace?"

Answers (a) and (b) are different.