3 The lengths of fish of a certain type have a normal distribution with mean 38 cm . It is found that \(5 \%\) of the fish are longer than 50 cm .
- Find the standard deviation.
- When fish are chosen for sale, those shorter than 30 cm are rejected. Find the proportion of fish rejected.
- 9 fish are chosen at random. Find the probability that at least one of them is longer than 50 cm .