Answer:
The 90% confidence interval for the mean time to graduate with a bachelor’s degree is (4.32, 4.84).
Yes, this confidence interval contradict the belief that it takes 4 years to complete a bachelor’s degree.
Step-by-step explanation:
The (1 - <em>α</em>)% confidence interval for population mean <em>μ, </em>when the population standard deviation is not known is:
![CI=\bar x\pm t_{\alpha/2, (n-1)}\times \frac{s}{\sqrt{n}}](https://tex.z-dn.net/?f=CI%3D%5Cbar%20x%5Cpm%20t_%7B%5Calpha%2F2%2C%20%28n-1%29%7D%5Ctimes%20%5Cfrac%7Bs%7D%7B%5Csqrt%7Bn%7D%7D)
The information provided is:
![\bar x=4.58\\s=1.10\\\alpha =0.10](https://tex.z-dn.net/?f=%5Cbar%20x%3D4.58%5C%5Cs%3D1.10%5C%5C%5Calpha%20%3D0.10)
Compute the critical value of <em>t</em> for 90% confidence interval and (n - 1) degrees of freedom as follows:
![t_{\alpha/2, (n-1)}=t_{0.10/2, (50-1)}=t_{0.05, 49}=1.671](https://tex.z-dn.net/?f=t_%7B%5Calpha%2F2%2C%20%28n-1%29%7D%3Dt_%7B0.10%2F2%2C%20%2850-1%29%7D%3Dt_%7B0.05%2C%2049%7D%3D1.671)
*Use a <em>t</em>-table for the probability.
Compute the 90% confidence interval for population mean <em>μ</em> as follows:
![CI=\bar x\pm t_{\alpha/2, (n-1)}\times \frac{s}{\sqrt{n}}](https://tex.z-dn.net/?f=CI%3D%5Cbar%20x%5Cpm%20t_%7B%5Calpha%2F2%2C%20%28n-1%29%7D%5Ctimes%20%5Cfrac%7Bs%7D%7B%5Csqrt%7Bn%7D%7D)
![=4.58\pm 1.671\times \frac{1.10}{\sqrt{50}}\\=4.58\pm 0.26\\=(4.32, 4.84)](https://tex.z-dn.net/?f=%3D4.58%5Cpm%201.671%5Ctimes%20%5Cfrac%7B1.10%7D%7B%5Csqrt%7B50%7D%7D%5C%5C%3D4.58%5Cpm%200.26%5C%5C%3D%284.32%2C%204.84%29)
Thus, the 90% confidence interval for the mean time to graduate with a bachelor’s degree is (4.32, 4.84).
If a hypothesis test is conducted to determine whether it takes 4 years to complete a bachelor’s degree or not, the hypothesis will be:
<em>Hₐ</em>:<em> </em>The mean time it takes to complete a bachelor’s degree is 4 years, i.e. <em>μ </em>= 4.
<em>Hₐ</em>:<em> </em>The mean time it takes to complete a bachelor’s degree is different from 4 years, i.e. <em>μ </em>≠ 4.
The decision rule based on a confidence interval will be:
Reject the null hypothesis if the null value is not included in the interval.
The 90% confidence interval for the mean time to graduate with a bachelor’s degree is (4.32 years, 4.84 years).
The null value, i.e. <em>μ </em>= 4 is not included in the interval.
The null hypothesis will be rejected at 10% level of significance.
Thus, it can be concluded that that time it takes to complete a bachelor’s degree is different from 4 years.