Interview Question: Playing Dice

Sample Question #249 (probability)
 
How many times do you need to throw a fair die so you get a 50% chance of seeing at least one "1"?
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2 Responses to Interview Question: Playing Dice

  1. Brett says:

    ANSWER
     
    The probability is 1 – Pr(throwing n dice and never getting a "1").  The latter probability is just (5/6)^n.  If you do the math, you’ll see the closest integer solution if n=4.
     
    (Comment: this question is similar to the people-sharing-at-least-one-birthday problem)
     

  2. Icedragon says:

    My answer is [ln(1/2)/ln(5/6)]+1=4. Is it right?

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