Respuesta :
Solution
- This is a Binomial probability question. The formula for Binomial probability is:
[tex]\begin{gathered} P(r)=\sum\text{ }^nC_rp^rq^{n-r} \\ where, \\ n=The\text{ total number of trials} \\ r=\text{ The number of successful trials\lparen where answer is correct\rparen} \\ p=\text{ The probability of success \lparen The probability of getting a question } \\ right) \end{gathered}[/tex]- We have been given:
[tex]\begin{gathered} n=7 \\ \text{ since there can only be two answers, it means that the} \\ \text{ probability of getting a question correct is:} \\ p=\frac{1}{2} \\ q=1-p=\frac{1}{2} \\ \\ \text{ The probability of getting at least 1 question wrong means the } \\ probability\text{ of getting 1, 2, 3, 4, 5, 6, or 7 question wrong.} \\ \\ \text{ Instead of calculating all these probabilities, we can simply say} \\ P(1)+P(2)+P(3)+P(4)+P(5)+P(6)+P(7)=1-P(0) \end{gathered}[/tex]- Thus, we have:
[tex]\begin{gathered} P(0)=^7C_0(\frac{1}{2})^0(\frac{1}{2})^7 \\ P(0)=\frac{1}{128} \\ \\ 1-P(0)=1-\frac{1}{128}=\frac{127}{128} \end{gathered}[/tex]Final Answer
The answer is
[tex]\frac{127}{128}[/tex]