Question

The least number of times a fair coin is to be tossed in order that the probability of getting atleast one head is at least $0.99$ is

• A. $5$
• B. $6$
• C. $7$
• D. $8$

Answer 1

Answer: (C)

$7$

$P(x=r)=\left(\frac{n}{r}\right)\ast {\frac{1}{2}}^{n}Now,1-P(x=0)\ge 0.99P(x=0)\le 0.01{\frac{1}{2}}^n\le 0.01n=7$