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

 Turn your calculator on Press . (You can see ON written in white to the right of the AC key.) Clearing the memory Press (You should see SAC above the key.)

 Entering data one variable Press (you'll see SD is the upper right corner of the screen). Enter the first number in your list and press . Enter the second number in your list and press . Continue until you're done with your list. two variables The 250HC does not do two-variable statistics.

 Calculating one-variable statistics mean (x) Press (you should see x above the key). standard deviation for populations (s or sn) Press (sn appears above the key). standard deviation for samples (s or sn-1) Press (sn-1 appears above the key).

 Calculating two-variable statistics r (correlation) The 250HC does not do two-variable statistics. regression coefficients slope The 250HC does not do two-variable statistics. y-intercept The 250HC does not do two-variable statistics.

 Calculating combinations and permutations combinations (nCr) Enter the n value. Press (you should see nCr above the key). Enter the r value and press . permutations (nPr) Enter the n value. Press (you should see nCr above the key). Enter the r value and press .

 Turning the calculator off Press .

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 (SAC) 2: Enter the data 3: Compute the mean (x) 4: Compute the population standard deviation. (sn) 5: Compute the sample standard deviation: (sn-1)

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

C: Find 10C6 and 9P5.
 1: Compute 10C6 (nCr) 2: Compute 9P5 (nPr)

You should get 10C6 = 210 and 9P5= 15120.

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