AP Statistics Review. Inference for Means (C23-C25 BVD ). Unless the standard deviation of a population is known, a normal model is not appropriate for inference about means. Instead, the appropriate model is called a t-distribution .
Inference for Means (C23-C25 BVD)
Plug in desired ME (like within 5 inches means ME = 5).
Plug in z* for desired level of confidence (you can’t use t* because you don’t know df).
Plug in standard deviation (from a sample or a believed true value, etc. Solve equation for n.