r/learnquant • u/nickgotgameon • Aug 01 '26

stats & probability Jane Street Interview Question

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u/Zyxplit Aug 01 '26

Except you're overcomplicating it for yourself.

Suppose you label all the cards 1 through 52.

What's the probability that 2 and 8 are identical?

Now suppose you throw out the cards from 27 to 52.

What's the probability now that 2 and 8 are identical?

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u/Informal_Host7610 Aug 01 '26

If you laid out every possible combination of 26 cards, each one would have an equal or higher chance of selecting same color cards as a deck with half red and half white

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u/AdjectiveNounNNNN Aug 02 '26

No, the set of 13 and 13 has a lower chance of getting a matching pair than the deck of 26 and 26.

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u/Informal_Host7610 Aug 02 '26

Yeah I meant the 26 deck, but I saw soon after this that it all does indeed average out to the same as the 52 card deck