Question: The life expectancy of a certain brand of laptop PC is normally distributed with a mean of 48 months and a standard deviation of 8 months.

a. (3) What is the probability that a randomly selected laptop of this brand will be in working condition after 5 years (Hint: the PC must work at least 60 months)?

b. (3) What percentage of the laptop PC of this brand will last less than 50 months?

c. (3) If the manufacturer guarantees the laptops for three years (and will replace them if they malfunction), what percentage of laptops will needed to be replaced?

d. (3) 95% of the laptops of this brand will have a life expectancy of at least how many months? (Hint: at what point will 5% of the laptops have malfunctioned?)