The life span of an imported brand of kettles sold by an appliance giant is normally distributed with a mean of 96 months and a standard deviation of 12 months.
1. What percentage of these kettles will last between 90 and 110 months?
2. The appliance giant offers a replacement guarantee on kettles which malfunction within a certain time of the purchase, but due to financial constraints, can only afford a maximum of 5% replacements. What must the guarantee period be?