Assume that the life expectancy of U.S. males is normally distributed with a mean of 80 years and a standard deviation of 4 years. What is the probability that a randomly selected male will live more than 85 years?

Answer 1

It depends on when the male is selected. If at birth, then you can use the normal distribution, mean above, with std deviation 4, and you see 85 is just slightly over one standard deviation.

But if the male is selected after birth, it changes, and you need to think on that. For instance, what if the male is now 90? 84? 50? Those gents will have a probablity greater than if chosen at birth.

Answer 2

Z = (x - μ)/SD = (85 - 80)/4 = 1.25

Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion related to that Z score.

If the man is now 90, the probability = 1 (certainty).

Answer 3

which of of the following stateements are correct?
a. A normal distribution is any distribution that is not normal
b. the graph of a normal distribution is bell-shaped
c. If a population has a normal distribution, the mean and the median are not equal
d. The graph of a normal distribution is symmetric