The average monthly gasoline purchase for a family with 2 cars is 90 gallons. This statistic has a normal distribution with a standard deviation of 10 gallons. A family is chosen at random.
(a) Find the probability that the family's monthly gasoline purchases will be between 86 and 96 gallons.
(b) Find the probability that the family's monthly gasoline purchases will be less than 87 gallons.
(c) Find the probability that the family's monthly gasoline purchases will be more than 75 gallons.