A die is thrown 6 times. If "getting an odd number" is a "success", what is the probability of 5 successes? |
$\frac{3}{64}$ $\frac{5}{64}$ $\frac{3}{32}$ $\frac{5}{32}$ |
$\frac{3}{32}$ |
The correct answer is Option (3) → $\frac{3}{32}$ When a die is thrown, sample space = $\{1, 2, 3, 4, 5, 6\}$. It has six equally likely outcomes. Probability of success = P(getting an odd number) = $p =\frac{3}{6}=\frac{1}{2}$, so $q = 1-\frac{1}{2}=\frac{1}{2}$ As the die is thrown 6 times, so there are 6 trials. Thus, we have a binomial distribution with $n = 6, p = \frac{1}{2}, q = \frac{1}{2}$. $P(r) = {^nC}_rp^rq^{n-r}= {^6C}_r(\frac{1}{2})^r(\frac{1}{2})^{6-r} = {^6C}_r(\frac{1}{2})^6$ for $r=0,1,2,....,6$ Probability of getting exactly 5 successes $=P(5)={^6C}_5(\frac{1}{2})^6=\frac{6}{2^6}=\frac{6}{64}=\frac{3}{32}$ |