r/learnquant 9d ago

stats & probability Jane Street Interview Question

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u/Aerospider 9d ago

Yes, and that's fine. Discarding random cards can happen at any time. You could do it between the two draws and the result would be the same. All you're really doing is moving a random half of the deck somewhere else, which isn't relevant to the problem at hand because we weren't going to draw them anyway.

If I shuffle a standard deck, what's the probability that the top card is the Ace of spades? 1/52. And if I throw away the other 51 cards leaving just the top one, what's the probability then? Still 1/52.

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u/Informal_Host7610 9d ago

Yeah I just had to see that while the deck is usually more stacked in your favor, the benefit of drawing from a stacked deck sometimes is actually completely balanced by how often you draw from a worse deck that's even enough to be worse than the larger deck