# Confidence Intervals for the Normal Distribution and T by morgossi7a8

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```									     Confidence Intervals for the Normal Distribution and T-Distribution

Use these functions to calculate Confidence Intervals
for One Variable Stats

On the TI-83 use the functions ZInterval and TInterval
On the TI-86 use the functions Zint1 and Tint1

Where are the functions on the calculator?
•     To access the functions on the TI-83, press STAT TESTS then 7:Ainterval or
8:TInterval
•     To access the functions on the TI-86, press 2nd MATH MORE then select STAT then TESTS
then MORE then select Zint1 or Tint1
The ungrouped raw data may be put in L1 as a single list or grouped data may be put in L1 and L2 as when doing
standard deviations, etc. On most exercises, the Stats (mean, etc.) are entered instead of the raw or grouped data. The
ZInterval screens are similar to the TInterval screens so only the ZInterval screens will be shown on this document.

ZInterval Screens for Data and Stats Input
TI-83                                                                      TI-86

Data Screen - Stats Screen

CONFIDENCE INTERVAL for a ZINTERVAL (The sample size n is 30 or greater)

EXAMPLE) Find a 90% Confidence interval (Z-interval) for a sample of size n = 30, a standard deviation of 6 and a mean
of 50.
The screens for Z and T-Intervals are almost identical on both calculators, so the TI-83 screens only will be shown. The
only difference: To execute the calculation on the TI-83, put the pointer on "Calculate" and then press ENTER. On the TI-
86, press <F1> to calculate.

To do the above example, enter the data as in the screens below. Then initiate the calculation as immediately above.
That's all there is to it! Use the population or sample standard deviation - not the sampling distribution standard deviation
- the calculator will calculate the proper standard deviation to use from the population or sample standard deviation that
you enter (note: you will be given either the population standard deviation or the sample standard deviation).

T-Intervals are done
the same way and are
used when the sample
size is less than 30 and
the population standard
deviation is not known.                                                                         90% Confidence Interval.
There's a 90% chance that
the above interval will contain
the population mean. 10% of
the time we will be wrong.

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