Final answer:
The critical t-value for a 90% confidence interval with 20 degrees of freedom is approximately 1.325.
Step-by-step explanation:
In this case, we need to find the critical t-value that corresponds to a 90% confidence interval.
Given that we have 20 degrees of freedom, we can refer to the t-distribution table or use a calculator to determine the critical value.
From the table, the critical t-value for a 90% confidence interval and 20 degrees of freedom is approximately 1.325.
Therefore, the correct answer is d) 1.325.