Jane Street

Interview Question

Quantitative Trader Intern Interview
Jane Street

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?

Unlock the Full Solution

Enter your email to get instant access to the complete solution, explanation, and similar practice problems.

Insights on 100+ quant firms, understand where to apply, and maximize your chances.

Get the official 2025 QB Quant Firm Tier List

Check your email inbox — you should get the interview in 1-2 minutes!