You are analyzing the sample of inverter batteries in Exercise 21. 

The population standard deviation of the batteries’ reserve capacities should be less than 0.50 hour. Does the confidence interval you constructed for σ suggest that the variation in the batteries’ reserve capacities is at an acceptable level? Explain your reasoning.

Data from Exercises 21

The reserve capacities (in hours) of 18 randomly selected inverter batteries have a sample standard deviation of 0.40 hour. Use a 90% level of confidence.