Statistics
posted by Dawn .
63.4 65.0 64.4 63.3 54.8 64.5 60.8 49.1 51.0
Assume that these observations are an SRS from the late Cretaceous atmosphere. What is the mean percent of nitrogen in ancient air with a 90% confidence level?
Hint: uses onesample t confidence

Formula: CI90 = mean + or  (tvalue)(sd/√n)
Determine the tvalue from a ttable. Use degrees of freedom 8 (which is sample size minus one). You will also need to determine the mean by adding up the values and dividing them by the sample size. Find sd (standard deviation) as well. Substitute those values into the formula to calculate the confidence interval.
I hope this will help get you started.