15. A researcher wants to determine the sample size necessary to
adequately conduct a study to estimate the population mean to within
5 points. The range of population values is 80 and the researcher plans
to use a 90% level of confidence. The sample size should be at least
______
16. The mean life of a particular brand of light bulb is 1200 hours. If
you know that at about 95% of this brand of bulbs will last between
1100 and 1300 hours, then what is the standard deviation of the light
bulbs’ life?
17. Completion time (from start to finish) of a building remodeling
project is normally distributed with a mean of 200 work-days and a
standard deviation of 10 work-days. To be 99% sure that we will not
be late in completing the project, we should request a completion time
of ______ work-day.
18. A large industrial firm allows a discount on any invoice that is
paid within 30 days. Of all invoices, 10% receive the discount. In a
company audit, 10 invoices are sampled at random. The probability
that fewer than 3 of the 10 sampled invoices receive the discount is
approximately_______________.
19. Suppose a population has a mean of 400 and a standard deviation
of 24. If a random sample of size 144 is drawn from the population,
the probability of drawing a sample with a mean less than 402 is
_______
20. If x is a binomial random variable with n=10 and p=0.8, what is
the probability that x is equal to 4 ?
21. The normal distribution is used to test about a population mean
for large samples if the population standard deviation is known.
"Large" is usually defined as _______
22. Lucy Baker is analyzing demographic characteristics of two
television programs, Americandol (population 1) and 60
Minutes (population 2). Previous studies indicate no difference in the
ages of the two audiences (The mean age of each audience is the
same.) Lucy plans to test this hypothesis using a random sample of
100 from each audience. Her null hypothesis is