Butter is sold in packs marked as salted or unsalted and the masses of the packs of both types of butter are known to be normally distributed. The mean mass of the salted packs of butter is...

Butter is sold in packs marked as salted or unsalted and the masses of the packs of both types of butter are known to be normally distributed. The mean mass of the salted packs of butter is 225.38 grams and the standard deviation for both packs is 8.45 grams.

A sample of 12 of the unsalted packs of butter had masses ,measured to the nearest gram , as follows, 219,226,217,224,223,216,221228,215,229,225,229

(a) find a 95%confidence interval for the mean mass of unsalted packs of butter.

(b) using the given data for salted packs, that is the mean and standard deviation, calculate limits between which 90% of the masses of salted packs of butter will lie.