A random sample of 17 American marriages found that their mean length was 9.4 years with a standard deviation of 8.1 years. (a) At the 5% level of significance can we conclude that the mean length of...

A random sample of 17 American marriages found that their mean length was 9.4 years with a standard deviation of 8.1

years.
(a) At the 5% level of significance can we conclude that the mean length of all American marriages is less than 10 years?

State and test appropriate hypotheses. State conclusions.
(b) What assumption is needed for the above analysis to be appropriate?