Confidence Interval Calculator: https://www.statssolver.com/confidence-interval.html
NOTE: Margin of error should be 1.6 (not 2.6).
For confidence intervals of the population mean: σ unknown, the main difference is that instead of using the z distribution, the t distribution is used. The t distribution is a family of probability distributions, with each individual t distribution depending on the degrees of freedom. Degrees of freedom refers to the number of independent pieces of information that go into computing the sample standard deviation. There are n-1 independent pieces of information because we know that the sum of the deviation about the mean is always equal to zero. Thus, we use n-1 degrees of freedom when computing confidence intervals for the population mean when the population standard deviation is unknown.
