. a company manufactures car batteries with an average life span of 2 or more years. an engineer believes this value to be less. using 40 samples, he measures the average life span to be 1.9 years with a standard deviation of 0.17. 1. State the null and alternative hypothesis.
2. At a 99% confidence level, is there enough evidence to discard the null hypothesis?
3. Do you need to use a z- test or t-test?
4. What type of test would you use - one tail or two tail?