Calculating Percentiles in Normal Distribution using TI-84 Calculator, Schemes and Mind Maps of Business Statistics

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Calculating Normal Curve

Percentiles on the TI-

These instructions will work for the TI-83 and TI-84 families of calculators.

Draw a picture illustrating the problem.

Since percentile is the area to the left of the score, we use the normalcdf function to calculate the area.

Remember to enter the important

numbers into the calculator in order. The

rule is:

First: Lower boundary = -

Second: Upper boundary = 215

Third: Average = 300

Fourth: Standard Deviation = 50

We’ll go through this keystroke by

keystroke.

Then press VARS to access the DISTR menu.

IMPORTANT!!

You must choose

the normalcdf

function, not the

normalpdf. Do not

ever use

normalpdf!!

Our answer is .045, so we round this to the 4th percentile.

Now, suppose we want to know the raw score for someone who scored at the 53rd^ percentile.

For this we use the invNorm function. Access the DISTR menu again and choose option 3:invNorm(

We get a result of 303.7. It makes sense to round this to 304.

Someone who scored 304 is at the 53rd percentile.