7 A factory makes water pistols, \(8 \%\) of which do not work properly.
- A random sample of 19 water pistols is taken. Find the probability that at most 2 do not work properly.
- In a random sample of \(n\) water pistols, the probability that at least one does not work properly is greater than 0.9 . Find the smallest possible value of \(n\).
- A random sample of 1800 water pistols is taken. Use an approximation to find the probability that there are at least 152 that do not work properly.
- Justify the use of your approximation in part (iii).