# Mean and Standard Deviation on a TI-85

Here's how to compute some basic statistics on your TI-85:
1. Press the [STAT] button. You should see something like this on your screen:
2. Press the [EDIT] button (that is, press the button on your calculator below the box labeled "EDIT" on the screen). Now your screen should look something like:
3. Press [ENTER] twice to indicate that you will keep your data in the list(s) xStat and yStat.
• If by some chance the screen shows some other entries for "xlist Name" or "ylist Name", you can always find xStat and yStat on the bottom menu on the screen, and re-enter them as list names. If needed, press the [MORE] button to get xStat and yStat on the bottom menu.
4. Now your screen should look something like this:  or  . If there are numbers already entered for x1, etc, clear them out by pressing [CLRxy] from the bottom menu, so that you have the second picture above.
5. Now type in your list of numbers, pressing [ENTER][ENTER]after each one. The idea of pressing [ENTER]twice is that we want our data values only on the "x" lines. The "y" lines should have "1" in them. For instance, if your list of numbers is {1,3,4,5,7}, then when you are done, your screen should look like this:   [Note: You do not have to enter the numbers in order]
6. Check over your list and make sure you have typed it correctly. You can delete or insert entries with the [DELi] or the [INSi] keys from the screen's bottom menu. You can scroll through the entries using the  and  keys.
7. Now we are ready to Calculate some statistics, so press [2nd][CALC] to get the calculate menu:

8. Again press [ENTER] twice to indicate that your data is in the list(s) xStat and yStat. Then the screen will change slightly to:
9. Now press [1-VAR] to indicate you want to calculate some one-variable statistics for your list. The screen now looks like:
10. The =4 tells you the mean of your list is 4. The x=2 tells you the [population] standard deviation of your list is 2.

### Short summary:

• To Enter data: Press [STAT] and select EDIT to enter your list of numbers. For what we do in this class, always using xStat and yStat will be fine. Use [CLRxy] if needed to clear out old data. Remember to enter your numbers on the "x" rows and leave the y's equal to 1.
• To Calculate some Statistics: press [2nd][CALC] and [ENTER] twice to use the xStat/yStat lists. Press 1-VAR to calculate.

### Test yourself:

Try to get the mean and standard deviation of   37.75, 38, 37, 38.5, and 37.5. You should get a mean of 37.75 and a standard deviation of 0.5.

## Bonus Topics:

### Frequency tables:

If you have many repeated data items, such as a frequency table:

 data item frequency 3 4 8 5 1 7 5 1

...meaning that your list contains four 3's, five 8's, etc., then you can enter the data items as x's and the corresponding frequencies as y's on the EDIT screen. For this list, you would start like this:

Finish entering the data, then ask the calculator to calculate 1-variable statistics as before:

### Help with medians:

Once you type a list of numbers into the data editor (see steps #1- #6 above):  you can press [SORTX] and you will find the x's are now displayed in ascending order, making it easier to pick out the median.