Answer:
The 90% confidence interval for the population mean gpa is [2.526,2.894].
Step-by-step explanation:
The confidence interval for population mean is

Where, μ is population mean, σ is standard deviation, z* is the value of z-score and n is number of samples.
The z-score value for 90% confidence interval is 1.645.
The average gpa is found to be 2.71, so μ=2.71. The variance is 0.25, it means


The 90% confidence interval for population mean is

![[2.71-1.645\cdot \frac{0.5}{\sqrt{20}},2.71+1.645\cdot \frac{0.5}{\sqrt{20}}]](https://tex.z-dn.net/?f=%5B2.71-1.645%5Ccdot%20%5Cfrac%7B0.5%7D%7B%5Csqrt%7B20%7D%7D%2C2.71%2B1.645%5Ccdot%20%5Cfrac%7B0.5%7D%7B%5Csqrt%7B20%7D%7D%5D)
![[2.526,2.894]](https://tex.z-dn.net/?f=%5B2.526%2C2.894%5D)
Therefore the 90% confidence interval for the population mean gpa is [2.526,2.894].