a.
To find: The percent of the vote does the sample suggest this candidate will get.
According to the sample, candidate will get 52% of votes.
Given information:
Confidence level: 95%
In a random sample of 625 registered voters, 325 of them express a preference for a candidate.
Calculation:
To compute the percentage of the vote the candidate will get by using sample, divide 325 by 625 multiply by 100.
The required percentage is 52%.
b.
To find: The standard deviation of the number of supporters that pollsters might find in
samples this size.
The standard deviation is 12.49.
Given information:
Confidence level: 95%
In a random sample of 625 registered voters, 325 of them express a preference for a candidate.
Calculation:
Let p be the proportion of votes to the candidate.
The estimated value for p is 0.52, then
The computation of standard deviation is shown.
Hence, the standard deviation is 12.49.
c.
To verify : A normal model is appropriate here.
It is verified that a normal model is appropriate here.
Given information:
Confidence level: 95%
In a random sample of 625 registered voters, 325 of them express a preference for a candidate.
Concept used:
If we expect at least 10 successes and 10 failures
Explanation:
Since
And
Thus, it can follow normal distribution.
d.
To find : The margin of error.
The margin of error is about 4%.
Given information:
Confidence level: 95%
In a random sample of 625 registered voters, 325 of them express a preference for a candidate.
Explanation:
The z -value for 95% confidence interval is 1.96.
The computation of margin of error is shown.
e.
To explain : The pollsters might say this election is “too close to call.”
Since the margin of error is so small implies results from sample are closer to the reality.
Given information:
Confidence level: 95%
In a random sample of 625 registered voters, 325 of them express a preference for a candidate.
Explanation:
Lesser the margin of error, more the confidence on the results.
Since the margin of error is so small implies results from sample are closer to the reality.
Chapter 10 Solutions
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