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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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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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)

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