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请教一道math题

A contest will consist of n questions, each of which is to be answwered either true or false, anyone who answer all n questions correstly will be a winner. what's the least value of n for which the probability is less than 1/1000 that a person who randomly guesses the answer to each question will be a winner?

5    10    50     100     1000    key: 10

请大家指点!

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每题猜对的概率二分之一,总共n 题全猜对的概率是

(1/2)^n < 1/1000

n=10 时   ((1/2)^5)^2 = 1/(32*32) = 1/1024 < 1/1000

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明白啦。谢谢!!

看来还是对题目没有理解

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