Question 1171912
The 90% half-interval is t(0.95,df=14)*s/sqrt(n)
this is 1.761*85/sqrt(15)=38.65
the 90% CI is then (1134.35, 1211.65)
Because mu was 1143, and mu lies within the CI, there is no evidence that the results obtained are due to a change in the mean, or that there is now a new distribution with a new mean.  Said another way, we would fail to reject Ho. We are highly confident (90%) that the true mean lies within this interval.