rishi2377 wrote:

A contest will consist of n questions and each question to be answered either ‘true’ or ‘false’. Anyone who answers all questions correctly will be the winner. What is 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 the winner?

A. 5

B. 10

C. 50

D. 100

E. 1000

Please explain. OA to follow shortly.

Probability of answering a Question right = 1/2

N Questions is 1/2 X 1/2 X 1/2 ... n times means (1/2) ^ n

We need to find least n such that (1/2) ^ n 1/1000

n =10 1/1024 < 1/1000

Hence B

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