I am studying statistics and found the following problem.
What is the probability that $2$ of the $10$ packets tested would turn out to be defective?
The problem should be solved using following formula $10C2 \cdot p^2 (1-p)^8$.
Now I am facing problem while trying to figure out the value of $p$. If one packet is picked at random then the probability of getting one defective packet $= 0.5$. Hence I have put $p=0.5$ in the above question and calculated the solution.
But in the solution they used $p=0.05$. I am not sure why $p$ should be $0.05$. Can you please help me on this.
Thanks in advance.