TI-84: Finding the Critical Value Using Inverse T

Using the TI-84 to find a critical value for a confidence interval for the mean when sigma is unknown.

[@nicholashurt9016]

why is is .975 instead of .95

[@bradenroark7528]

because each side equals the remaining .5 so you gotta divide that by 2

[@Killer342127]

did not explain entirely what i needed

[@Eric_Generic]

Super helpful and clear explanation!

[@chrisclements3862]

how about 2 tailed? thank you

[@twosigma1371]

First divide alpha in two to get the area in one tail then use the inverse t. For example, if alpha is 0.05, then there would be 0.025 amount of area in each tail. You can use inverse t with an input of 0.025 and get the negative t-value or use an input area of 0.975 to get the upper t-value (since there would be a cumulative area of 0.975 to the left of the upper t-value). The inverse-t function expects a cumulative area and degrees of freedom (n-1) as the input.

[@chrisclements3862]

@@twosigma1371 Perfect thank you so much