Answer:
(a) The proportion of tenth graders reading at or below the eighth grade level is 0.1673.
(b) The 95% confidence interval for the population proportion of tenth graders reading at or below the eighth grade level is (0.198, 0.260).
Step-by-step explanation:
Let <em>X</em> = number of students who read above the eighth grade level.
(a)
A sample of <em>n</em> = 269 students are selected. Of these 269 students, <em>X</em> = 224 students who can read above the eighth grade level.
Compute the proportion of students who can read above the eighth grade level as follows:
![\hat p=\frac{X}{n}=\frac{224}{269}=0.8327](https://tex.z-dn.net/?f=%5Chat%20p%3D%5Cfrac%7BX%7D%7Bn%7D%3D%5Cfrac%7B224%7D%7B269%7D%3D0.8327)
The proportion of students who can read above the eighth grade level is 0.8327.
Compute the proportion of tenth graders reading at or below the eighth grade level as follows:
![1-\hat p=1-0.8327](https://tex.z-dn.net/?f=1-%5Chat%20p%3D1-0.8327)
![=0.1673](https://tex.z-dn.net/?f=%3D0.1673)
Thus, the proportion of tenth graders reading at or below the eighth grade level is 0.1673.
(b)
the information provided is:
<em>n</em> = 709
<em>X</em> = 546
Compute the sample proportion of tenth graders reading at or below the eighth grade level as follows:
![\hat q=1-\hat p](https://tex.z-dn.net/?f=%5Chat%20q%3D1-%5Chat%20p)
![=1-\frac{X}{n}](https://tex.z-dn.net/?f=%3D1-%5Cfrac%7BX%7D%7Bn%7D)
![=1-\frac{546}{709}](https://tex.z-dn.net/?f=%3D1-%5Cfrac%7B546%7D%7B709%7D)
![=0.2299\\\approx 0.229](https://tex.z-dn.net/?f=%3D0.2299%5C%5C%5Capprox%200.229)
The critical value of <em>z</em> for 95% confidence interval is:
![z_{\alpha/2}=z_{0.05/2}=z_{0.025}=1.96](https://tex.z-dn.net/?f=z_%7B%5Calpha%2F2%7D%3Dz_%7B0.05%2F2%7D%3Dz_%7B0.025%7D%3D1.96)
Compute the 95% confidence interval for the population proportion as follows:
![CI=\hat p \pm z_{\alpha/2}\sqrt{\frac{\hat p(1-\hat p)}{n}}](https://tex.z-dn.net/?f=CI%3D%5Chat%20p%20%5Cpm%20z_%7B%5Calpha%2F2%7D%5Csqrt%7B%5Cfrac%7B%5Chat%20p%281-%5Chat%20p%29%7D%7Bn%7D%7D)
![=0.229\pm 1.96\times \sqrt{\frac{0.229(1-0.229)}{709}}\\=0.229\pm 0.03136\\=(0.19764, 0.26036)\\\approx (0.198, 0.260)](https://tex.z-dn.net/?f=%3D0.229%5Cpm%201.96%5Ctimes%20%5Csqrt%7B%5Cfrac%7B0.229%281-0.229%29%7D%7B709%7D%7D%5C%5C%3D0.229%5Cpm%200.03136%5C%5C%3D%280.19764%2C%200.26036%29%5C%5C%5Capprox%20%280.198%2C%200.260%29)
Thus, the 95% confidence interval for the population proportion of tenth graders reading at or below the eighth grade level is (0.198, 0.260).