Comparing the Normal and T Distribution

T Distributions have shorter peaks and fatter tails, especailly at low degrees of freedom. We look at the differences in finding critical values from confidence levels to create confidence intervals when using Z or T. We also learn how to use the different functions on the TI-84 Plus C including: normalcdf, tcdf, invNorm, and invT.

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For the invnorm, why don't you also subtract invnorm(.9) by invnorm(.1)? Wouldn't only using invnorm(.9) be 90% of the distribution?