Study conducted with groups of N=12 children each (sample size), to evaluate how long it takes to learn foreign language on a basic communication level. It was found that it takes them in average  Íx =30 days (sample average) with a sample standard deviation of s=5 days.

Construct a 90% confidence interval for the population mean for the time needed for children to learn basics of foreign language.

(Population standard deviation is not known. For Margin of Error use t-value from attached Appendix Table for t-Distribution)