Question 1183463
This will be a t-test with t (df=19) and the critical value of |t| being > 2.093 at the 0.05 level of significance.
Assuming random sample, normality, and s being estimator of sigma, and the "population mean" being 55 minutes, the past way.
t=(30-55)/1.5/sqrt(20)
=-74.5
This is highly significant for the population mean (the old procedure) being greater than the new procedure, or as would be stated here, the new procedure is shorter than the old one.