In: Statistics and Probability
The Aluminum Association reports that the average American uses 56.8 pounds of aluminum in a year. A random sample of 50 households is monitored for one year to determine aluminum usage. If the population standard deviation of annual usage is 12.3 pounds, what is the probability that the sample mean will be each of the following? Appendix A Statistical Tables
a. More than 60 pounds
d. Less than 55 pounds
We have given a random sample of
households aluminum usage is monitored which is large
, by the central limit theorem, the random variable
has an approximately normal distribution.
The population mean
with population standard deviation
.
Now using
as the Z-score for a given
value.
(a) Probability that sample mean
is more than 60 pounds.
So, the probability that the sample mean be more than 60 pounds
is calculated as
________________
(b) Probability that sample mean be less than 55 pounds
So the probability that the sample mean be less than 55 pounds is calculated as