If x-bar = 100 and s = 20 (units completely theoretical and unimportant) and n = 25, calculate a 95% confidence interval for the true population mean :

Lower limit (to two decimal places) is:

Upper limit (to two decimal places) is:

Value of t/Z used is:

Note: Z-test (1.96) is used when population variance is known, and t-test is used when population variance is unknown. Please justify which test you have used and explain why you have used either the Z-test or t-test. Also, don't just copy and paste it from other sources. I want to clarify and I want to learn this.

Reference: https://online.stat.psu.edu/stat415/lesson/10/10.1