426.Rolling Until It's Matched
★★★expected valueCh. 6 — Random Variables and Expectation444+ Problems in Probability
Francisco rolls a fair die and records the value. He then keeps rolling until he obtains a value at least as large as his first roll. Let be the number of rolls *after* the first. Find .
Sign in to submit an answer and track it toward your stats.
Sign inHint
Given the first roll is , the wait is geometric. Average over — a harmonic number appears.
Want timed drills, mental math, and a market-making game too? Try the full practice suite →