1.

A coin is tossed n times. The probability of getting head at least once is greater than `0.8.` Then the least value of n isA. 7B. 6C. 5D. 3

Answer» Correct Answer - D
Suppose the coin is tossed n times. Let X be the number of heads obtained. Then, X follows a binomial distribution with parameters n and `p=1//2`.
Now,
`P(Xge1)ge0.8`
`rArr 1-P(X=0)ge0.8`
`rArr 1-.^nC_(0)p^0(1-p)^nge 0.8`
`rArr ((1)/(2))^nle 0.2rArr ((1)/(2))^nle (1)/(5)rArr 2^nge 5rArr nge 3`
Hence, the least value of n is 3.


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