Rolls until an even sum
A fair -sided die is rolled repeatedly, keeping a running total, and you stop as soon as the running sum is even. What is the expected number of rolls?
Show hints (2)+
- First roll is even with probability (stop). Otherwise the sum is odd.
- From an odd sum, each roll makes it even with probability - a geometric wait, mean .
Answer
Reveal answer →Final answer
2
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Asked at: Optiver, Akuna Capital