5. The duration of the pregnancy of a certain breed of cow is normally distributed with mean \(\mu\) days and standard deviation \(\sigma\) days. Only \(2.5 \%\) of all pregnancies are shorter than 235 days and \(15 \%\) are longer than 286 days.

1. Show that \(\mu - 235 = 1.96 \sigma\).
2. Obtain a second equation in \(\mu\) and \(\sigma\).
3. Find the value of \(\mu\) and the value of \(\sigma\).
4. Find the values between which the middle \(68.3 \%\) of pregnancies lie.