A) 2
B) 3
C) 4
D) 5
Correct Answer: B
Solution :
Let X be the number of heads getting. X follows binomial distribution with parameters \[n,\,p=1/2\] Given that \[P(X\ge 1)\,\ge \,0.8\] Þ \[1-P(X=0)\ge 0.8\Rightarrow P(X=0)\le 0.2\] Þ\[^{n}{{C}_{0}}\,{{(1/2)}^{n}}\le \,0.2\,\] \[\Rightarrow \] \[\frac{1}{{{2}^{n}}}\le \frac{1}{5}\Rightarrow \,{{2}^{n}}=5.\] \[\therefore \]The least value of \[n\] is 3.
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