Jane Street–styleTrader InternQuantitative Trader InternQuestion #479
Suppose you have two urns that are indistinguishable from the outside. One urn contains 3 one-dollar coins and 7 ten-dollar coins. The other urn contains 5 one-dollar coins and 5 ten-dollar coins. You choose an urn at random and draw a coin at random. You find that it is a $10 coin. Now you have the option to draw again (without replacing the first coin) from either the same urn or the other urn. Should you draw from the same urn or switch to the other urn to maximize the probability of drawing another $10 coin?
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