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 is

Options

A. 2
B. 3
C. 4
D. 5

Answer

B

Explanation

Let X be the number of heads getting in n tosseds. X follows Binomial distribution with parameters, `n, p = (1)/(2) , q = (1)/(2)`
Given that, `P(X ge 1) le 08`
`rArr 1-P(X=0) ge 08`
`rArr P(X =0) le 02`
`rArr ""^(n)C_(0)((1)/(2))^(2) ((1)/(2))^(0) le02`
`rArr (1)/(2^(n)) le(1)/(5) rArr 2^(n) ge 5`
`therefore` The least value of n is 3.