The life (in months) of a hair dryer is approximately normally distributed with mean 96 and a standard deviation of 18. You are required to determine the following:

a) what percentage of the units sold will have to be replaced if the warranty period is five years?

b) The maximum warranty period if the manufacturer wants to limit the replacement to 1% of the units sold?

c) How many numbers of units will be sold in part (a) if there are 10 units in a shop?