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(X≥1)≥0.8
⇒1-P(X=0)≥0.8
⇒1-.nC0p0(1-p)n≥0.8
⇒(
1
2
)n≤0.2⇒(
1
2
)n≤
1
5
⇒2n≥5⇒n≥3
Hence, the least value of n is 3.
