Respuesta :
Answer:
The 80% confidence interval for the population proportion of tenth graders reading at or below the eighth grade level is (0.149, 0.207).
Step-by-step explanation:
In a sample with a number n of people surveyed with a probability of a success of [tex]\pi[/tex], and a confidence level of [tex]1-\alpha[/tex], we have the following confidence interval of proportions.
[tex]\pi \pm z\sqrt{\frac{\pi(1-\pi)}{n}}[/tex]
In which
z is the zscore that has a pvalue of [tex]1 - \frac{\alpha}{2}[/tex].
Suppose a sample of 292 tenth graders is drawn. Of the students sampled, 240 read above the eighth grade level.
So 292 - 240 = 52 read below or at eight grade level, and that [tex]n = 292, \pi = \frac{52}{292} = 0.178[/tex]
80% confidence level
So [tex]\alpha = 0.2[/tex], z is the value of Z that has a pvalue of [tex]1 - \frac{0.2}{2} = 0.9[/tex], so [tex]Z = 1.28[/tex].
The lower limit of this interval is:
[tex]\pi - z\sqrt{\frac{\pi(1-\pi)}{n}} = 0.178 - 1.28\sqrt{\frac{0.178*0.822}{292}} = 0.149[/tex]
The upper limit of this interval is:
[tex]\pi + z\sqrt{\frac{\pi(1-\pi)}{n}} = 0.178 + 1.28\sqrt{\frac{0.178*0.822}{292}} = 0.207[/tex]
The 80% confidence interval for the population proportion of tenth graders reading at or below the eighth grade level is (0.149, 0.207).
