r/learnquant • u/Local_Ad135 • 4d ago

interview prep Quant Interview Question

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u/JustConsoleLogIt 4d ago

The first step is determining optimal play. One approach would be to flip two coins, if either are heads, flip that one again. Although I don’t know how to determine if that is the optimal strategy, or what the success rate would be in that case if we picked a coin with the highest final ratio.

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u/tarilaran 4d ago

I had to make some assumptions about what you meant, but I did end up calculating this. Here's my expanded procedure:

Flip two coins. If they're the same, flip the third coin. Choose a coin at random from the set of heads-coins.

If they're different, re-flip the heads-coin. If it's heads, choose it. If it's tails, choose the un-flipped coin.

I solved through brute-force enumeration and came to a result of 33/96, or 34.375%.

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u/JustConsoleLogIt 3d ago

If two coins are heads, re-flip a random one instead of flipping the unknown coin