Questions / Quant trading, Counting & stopping
Wait for both faces
You repeatedly toss a fair coin. Including all tosses, what is the expected number needed to have seen both heads and tails?
Answer it in the app It's free. You get hints, a second try if you miss, and a follow-up question.
Show the answer and worked solution
Answer: 3 tosses
- The first toss takes one step. The opposite face then has probability 1/2 each toss and expected waiting time 2. Total: 3.
Interview shortcut. One toss shows a face, then wait 1/p = 2 for the other.
In the app this has a follow-up where one thing about the setup changes. Try the follow-up.