Problems on Normal Distribution
Directions: Draw a clearly labeled diagram and then solve each problem.
1. The gestation period (length of pregnancy) for male babies born in New York is
normally distributed with a mean of 39.4 weeks and a standard deviation of 2.43 weeks.
(a) What percent of mothers of male babies are pregnant for less than 35 weeks?
(b) What percent of mothers of male babies are pregnant for between 35 and 40
(c) What percent of mothers of male babies are pregnant for more than 40 weeks?
(d) Suppose a sailor had shore leave 46 weeks ago and his wife is delivering a baby
today. What should the sailor say to his wife when he gets home?
The daily demand for gas at Goodâ€™s Gas station is normally distributed with a mean
of 1812 gallons and a standard deviation of 254 gallons.
What is the probability that the demand for gas will exceed 2000 gallons on any
(b) What is the probability that the demand for gas in a day will be between 1500 and
(c) What is the probability that the demand for gas will exceed 1500 gallons on any
3. Suppose that the life of an Evercharged battery is normally distributed with a mean
life of 12 hours and a standard deviation of 0.72 hours. What percent of Evercharged
batteries will last:
a) less than 11.5 hours
b) more than 13 hours
c) between 11.5 and 13 hours?
4. Suppose that a school district wants to start a program for gifted students. The
participants in the program are to be chosen on the basis of IQ scores (normal
with = 100, = 15). If the school district wants only the top 2% of students to
participate in the program, what should be the IQ score that students must
exceed to be accepted?
5. In problem #2, how much gasoline should the station have on hand at the
beginning of the day so that the probability of running out of gas that day is only
6. 10% of Americans are left handed.
(a) If 6 people are selected at random, what is the probability that more than 3 of them
(b) Suppose a group of 600 mathematicians get together for a conference. What is the
probability that more than 80 of them are left-handed? (Use the normal approximation to
7. If a couple has five children, what is the probability that :
(a) they have three boys and two girls (b) all five are boys
more than 3 boys
(c) at least one is a girl
(d) they have
8.In a redundant communications network, there are 6 paths between two nodes, so that if a message can not get
through one path, it can be sent through one of the other paths. Suppose that the probability that an individual path
is busy is 80%. What is the probability that a message can be sent from one node to the other?
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