Answer:
a) We need a sample size of at least 705.
b) We need a sample size of at least 1692.
Step-by-step explanation:
In a sample with a number n of people surveyed with a probability of a success of , and a confidence level of , we have the following confidence interval of proportions.
In which
z is the zscore that has a pvalue of .
The margin of error is:
90% confidence level
So , z is the value of Z that has a pvalue of , so .
a) If she uses 1999 estimate of 11.8% obtained from the Current Population Survey.
We need a sample of size at least n
n is found when .
So
Rounding up
We need a sample size of at least 705.
b) She does not use any estimate.
Same thing as above, we just use when do not use any estimate.
Rounding up
We need a sample size of at least 1692.