The random variable X is normally distributed with mean \(\mu\) and standard deviation \(\frac{1}{4} \mu\). It is given that \(\text{P}(X > 20) = 0.04\).

1. Find \(\mu\).
2. Find \(\text{P}(10 < X < 20)\).
3. 250 independent observations of X are taken. Find the probability that at least 235 of them are less than 20.