Respuesta :
Answer: The confidence interval is (0.74, 0.78)
This can alternatively be written as 0.74 < p < 0.78
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Explanation:
n = 2500 = sample size
x = 1900 = number of successes = number who plan to vote
phat = x/n = 1900/2500 = 0.76
phat is the sample proportion that estimates the population proportion p.
At 95% confidence, the z critical value is roughly z = 1.96 which you use a table or calculator to find this value (or it's something you memorize).
E = margin of error
E = z*sqrt(phat*(1-phat)/n)
E = 1.96*sqrt(0.76*(1-0.76)/2500)
E = 0.016742 approximately
The lower bound (L) of the confidence interval is
L = phat - E
L = 0.76 - 0.016742
L = 0.743258
L = 0.74
The upper bound (U) of the confidence interval is
U = phat + E
U = 0.76 + 0.016742
U = 0.776742
U = 0.78
The values of L and U are approximate.
The confidence interval in the format (L, U) would be (0.74, 0.78) approximately.
Another way to write the confidence interval is to say 0.74 < p < 0.78 as it's in the form L < p < U; showing that we're 95% confident that p is somewhere between 0.74 and 0.78
In other words, we're 95% confident that between 74% and 78% of the population would plan to vote in the next presidential election.
