453.Fives Before the First Six
★★★expected valueCh. 6 — Random Variables and Expectation444+ Problems in Probability
A fair 6-sided die is rolled repeatedly until the first 6 appears. What is the expected number of 5s rolled before stopping?
Sign in to submit an answer and track it toward your stats.
Sign inHint
Ignore rolls of 1–4 entirely, or condition on which of 5 and 6 appears first, and recurse.
Want timed drills, mental math, and a market-making game too? Try the full practice suite →