Ashville City Maintenance Chief wants to cut back on the costs of maintaining the city automobile fleet. Knowing that the city cars are kept for only year, he feels that the city's periodic maintenance schedule may cost more than it is worth. He randomly selects a sample of 300 cars. Among those 300 cars, 75 cars receive no maintenance unless they break down. The rest of the cars are maintained using the usual schedule. At the end of the year he finds the results pertaining to average costs per vehicle in these two groups (shown below). What can you tell the Ashville City Maintenance Chief about this experiment: is the difference across groups statistically significant at 95% confidence level? Use the five step model to answer this question.

Variable "Costs per Vehicle":

No Maintenance                       Maintained Cars

= $625                                        = $575

S₁ = 150                                  S₂ = 200

N₁ = 75                                   N₂ = 225