[Math] Odds of guessing suit from a deck of cards, with perfect memory

probabilitystatistics

While teaching my daughter why drawing to an inside straight is almost always a bad idea, we stumbled upon what I think is a far more difficult problem:

You have a standard 52-card deck with 4 suits and I ask you to guess the suit of the top card. The odds of guessing the correct suit are obviously 1 in 4. You then guess again, but the first card is not returned to the deck. You guess a suit other than the first drawn and the odds are 13/51, somewhat better than 1 in 4.

Continuing through the deck your odds continually change (never worse than 1 in 4, definitely 100% for the last card) what are your overall odds for any given draw over the course of 52 picks?

Can this be calculated? Or do you need to devise a strategy and write a computer program to determine the answer? Do these type of problems have a name?

Dad and to a much less extent daughter, await your thoughts!

Best Answer

The approximate odds of guessing the suit properly is 35.4%, quite a bit higher than 25%. This is easy to calculate with Monte Carlo analysis, though that does not easily allow a more precise answer. A combination of elementary probability and MC would be best though I have not attempted this.

I can't immediately think of a good way to find the exact rational probability since there are many ways for the number of each suit to change throughout the draws. Perhaps a combinatorialist could help here?

Related Question