Probability/Statistics: You have two fair dice. What's the probability their sum is a prime number? (Work it out in 30 seconds) Three people play a game where each flips a coin. Last person with a different result wins. What's the expected number of flips? Mental Math: What's 17 x 23? (5 seconds to answer) Square root of 2907 to two decimal places? (20 seconds) If S&P moves 0.3% and AAPL beta is 1.2, what's AAPL's expected move? Programming/Algorithms: Write a function to find arbitrage opportunities in a currency exchange matrix Given real-time trade data, design an algorithm to detect wash trading Implement a fast moving median calculator for streaming data Market Knowledge: How would you arbitrage S&P 500 futures vs the underlying basket? What happens to options prices during earnings announcements? Design a mean-reversion strategy for ETF pairs trading Brain Teasers: 100 people with red/blue hats. Each can see others' hats but not their own. They must simultaneously guess their hat color. They can plan beforehand. Maximize group survival.