HMMT 2018 C5
- Combinatorics
- Answer
A bag contains nine blue marbles, ten ugly marbles, and one special marble. Ryan picks marbles randomly from this bag with replacement until he draws the special marble. He notices that none of the marbles he drew were ugly. Given this information, what is the expected value of the number of total marbles he drew?
Dataset text NuminaMath olympiads. Quoted with source.
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\frac{20}{11}
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