254.HHH Before HTH
★★★markov chainsOptiver
A fair coin is flipped repeatedly until either HHH or HTH appears. What is the probability that HHH comes first?
Sign in to submit an answer and track it toward your stats.
Sign inHint
Track the useful suffix you currently hold — nothing, H, HH or HT — and write one equation per state. Watch what a tail does to HH.
Want timed drills, mental math, and a market-making game too? Try the full practice suite →