The teacher kept track of how long it took students to finish a test. After 20 minutes, 3 students had finished the test.
1 answer:
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Answer: a) 15, b) 1.
Step-by-step explanation:
A researcher studying public opinion of proposed social security changes obtains a simple random sample of 35 adult Americans and asks them whether or not they support the proposed changes. To say that the distribution of the sample proportion of adults who respond yes, is approximately normal, how many more Americans does the researcher need to sample in the following cases?
(a) 10% of all adult Americans support the changes
Here,
And ,
So, consider the equality, to find the value of 'n'.
So, there are more adult Americans needed.
(b) 15% of all adult Americans supports the changes
Here,
So, again we get that
So, there are more adult Americans needed.
Hence, a) 15, b) 1.
Because it wouldn't let me edit my answer, I'll post all of my proofs here.
Answer:
A sample of 1068 is needed.
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:
95% confidence level
So , z is the value of Z that has a pvalue of
, so
.
At 95% confidence, how large a sample should be taken to obtain a margin of error of 0.03 for the estimation of a population proportion?
We need a sample of n.
n is found when M = 0.03.
We have no prior estimate of , so we use the worst case scenario, which is
Then
Rounding up
A sample of 1068 is needed.