For a time study, what would be the required number of readings if the analyst wanted to be 90% confident that the mean observed time was within +/-5% of the true mean and he established the following values for an element after observing 19 cycles: 0.09, 0.08, 0.10, 0.12, 0.09, 0.08, 0.09, 0.12, 0.11, 0.12, 0.09, 0.10, 0.12, 0.10, 0.08, 0.09, 0.10, 0.12, 0.09? You have a 5% desired acceptable fraction k (k = 0.05).

n = (t/k)²

n = number of observations needed

t = tabled value (t distribution table provided see Appendix)

= standard deviation

k = an acceptable fraction of the sample mean

= population mean