The position of the graphically represented keys can be found by moving your mouse on top of the graphic. 

Turn your calculator on
Press The AC Key: Row 1, Column 5. (It says ON on top of the key.)
Clearing the memory
Press The Second Key: Row 1, Column 1 It's yellow. The x factorial key: Row 3, Column 1, you should see CSR above the key. (CSR stands for Clear Statistical Registry)

 

Entering data
one variable
Enter a data element and press The Sigma Plus Key: Row 4, Column 1 (if you need to delete an element, type it in, then press The Second Key: Row 1, Column 1 It's yellow. The Sigma Plus Key: Row 4, Column 1. The screen will tell you how many numbers you've entered. Do the same with the rest of the list. 
two variables
The TI-25X does not do regression.

 

Calculating one-variable statistics
mean (x)
Press The Second Key: Row 1, Column 1 It's yellow. The STOre Key: Row 5, Column 1.  You should see x over the key.
standard deviation for populations (s or sn)
Press The Second Key: Row 1, Column 1 It's yellow. The Sum Key: Row 7, Column 1. You should see sn over the key.
standard deviation for samples (s or sn-1)
Press The Second Key: Row 1, Column 1 It's yellow. The R C L (Recall) Key: Row 6, Column 1. You should see sn-1 over the key.

Calculating two-variable statistics
r (correlation)
The TI-25X cannot do correlation.
regression coefficients
slope
The TI-25X cannot do regression.
y-intercept
The TI-25X cannot do regression.


Calculating combinations and permutations
combinations (nCr)
The TI-25X cannot do combinations.
permutations (nPr)
The TI-25X cannot do permutations.

 

Turning the calculator off
This is a solar calculator. It does not turn off. (If you cover it, it will turn off by itself in about two minutes.)

 

Worked Out Examples

In the following examples, we list the exact key sequence used to find the answer.  We will list the keys by the main symbol on the key.  In parentheses, we will list a helpful mnemonic, e.g. we will list ex as (ex).


A: What is the mean and standard deviation of the following list of numbers?

15      16      20      21

1: Clear Memory  The Second Key: Row 1, Column 1 It's yellow. The x factorial key: Row 3, Column 1 (CSR) 
2: Enter Data   The One Key: Row 7, Column 2 The Five Key: Row 6, Column 3 The Sigma Plus Key: Row 4, Column 1 The One Key: Row 7, Column 2 The Six Key: Row 6, Column 4 The Sigma Plus Key: Row 4, Column 1
 The Two Key: Row 7, Column 3 The Zero Key: Row 8, Column 2 The Sigma Plus Key: Row 4, Column 1 The Two Key: Row 7, Column 3 The One Key: Row 7, Column 2 The Sigma Plus Key: Row 4, Column 1 
3: Compute the mean  The Second Key: Row 1, Column 1 It's yellow. The S T O (Store) Key: Row 5, Column 1 ( x )
4: Compute the standard deviation (population)  The Second Key: Row 1, Column 1 It's yellow. The Sum Key: Row 7, Column 1 (sn)
5: Compute the standard deviation (sample)  The Second Key: Row 1, Column 1 It's yellow. The R C L (Recall) Key: Row 6, Column 1 (sn-1)


     You should get a mean of 18, population standard deviation of 2.549509757 and a sample standard deviation of 2.943920289.

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