The distribution of battery life of MacBook laptops is normally distributed with a mean of 8.4 hours and a standard deviation of 1.2 hours. The distribution of Dell laptops is normally distributed with a mean of 7.1 hours with a standard deviation of 0.75 hours. Required:
a. Calculate the probability that a randomly selected MacBook laptop battery lasts more than 9 hours.
b. Calculate the probability that a randomly selected Dell laptop battery lasts be- tween 5 and 8 hours.
c. How long must a MacBook laptop battery last to be in the top 4%?
d. How long must a Dell laptop battery last to be at the 40th percentile?
e. Calculate the probability that a randomly selected MacBook laptop lasts longer than the 25th percentile of Dell laptops.
f. A randomly selected laptop has a battery life of at least 8.0 hours. Calculate the probability of this laptop being a MacBook and the probability of it being a Dell.