Fri, 14 Feb 2020 06:00:42 GMT language
An atomic absorption method for the determination of the amount of iron present in used jet engine oil was found, from pooling 30 triplicate analyses, to have a s = 2.4 mg Fe/mL. If s is a good estimate of sigma, calculate the 80% and 95% confidence interval of the result, 18.5 mg Fe/mL, if it was based on
(a) single analysis, and
(b) the mean of four analyses.
I know the equation for it which is, CI = xbar +- zs/SqrtN. What I am confused about is the z. Is z a constant?