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Find the critical value of a t distribution

Please explain & show why you use formula you use.

Find the critical t alpha/2 assuming the population is normally distributed, the confidence level is 95%, n=101 and sigma is unknown.

The answer is 1.984-I'm having trouble with the large n. I don't have a TI-83 calculator. My book stops @ 29 then just says large z number on the t-dist. table. Don't know what to do with this number-this is the only chart I will have available on a test.

Solution Summary

In this solution I have given an overview of critical values for a t distribution. Secondly, I have explained how to use the Excel sheet I have included to calculate critical values. Finally I have explained why in some cases you can use the standard normal or z distribution to approximate a t distribution.