USE this rule
Crit > Calc = Cannot Reject = No Statistical difference in the means
Crit < Calc = Reject = Statistical difference in the means
Q1: Historically, my HRV fleet averaged 40,000 miles between breakdowns with a 8000 mile standard deviation. Implemented Continuous Improvement teams to research better inspection methods and after the kaizen, sampled, randomly 30 HRV cars and found 43,000 miles between service interruptions.
Test at the 0.05 Alpha I tail Z test and determine if the efforts paid off statistically