Answer :
a. The point estimate for the proportion of all entering freshmen at this college who scored more than 550 on the math SAT is 0.35.
b. The 98% confidence interval for the proportion of all entering freshmen at this college who scored more than 550 on the math SAT is [0.273, 0.427].
c. No, the confidence interval does not necessarily contradict the belief that the proportion at her university is also 39%. The confidence interval is a range of values that is likely to contain the true population proportion with a certain degree of confidence. The belief that the proportion is 39% falls within the confidence interval, so it is consistent with the sample data.
What is the point estimate and confidence interval for the proportion of entering freshmen who scored more than 550 on the math SAT at this college? Does the confidence interval support the belief that the proportion is 39%?
The college admissions officer sampled 120 entering freshmen and found that 42 of them scored more than 550 on the math SAT. Using this sample, we can estimate the proportion of all entering freshmen at this college who scored more than 550 on the math SAT. The point estimate is simply the proportion in the sample who scored more than 550 on the math SAT, which is 42/120 = 0.35.
To get a sense of how uncertain this point estimate is, we can construct a confidence interval. A confidence interval is a range of values that is likely to contain the true population proportion with a certain degree of confidence.
We can construct a 98% confidence interval for the proportion of all entering freshmen at this college who scored more than 550 on the math SAT using the formula:
point estimate ± (z-score) x (standard error)
where the standard error is the square root of [(point estimate) x (1 - point estimate) / sample size], and the z-score is the value from the standard normal distribution that corresponds to the desired level of confidence (in this case, 98%). Using the sample data, we get:
standard error = sqrt[(0.35 x 0.65) / 120] = 0.051
z-score = 2.33 (from a standard normal distribution table)
Therefore, the 98% confidence interval is:
0.35 ± 2.33 x 0.051 = [0.273, 0.427]
This means that we are 98% confident that the true population proportion of all entering freshmen at this college who scored more than 550 on the math SAT falls between 0.273 and 0.427.
Finally, we can compare the confidence interval to the belief that the proportion at her university is 39%. The confidence interval does not necessarily contradict this belief, as the belief falls within the interval. However, we cannot say for certain whether the true population proportion is exactly 39% or not, since the confidence interval is a range of plausible values.
Learn more about confidence intervals
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