## Why You Should Use a TI-89 Graphing Calculator for Statistics

The TI graphing calculators are recommended for AP statistics (and are allowed to be taken into exams). You can get one on Amazon.com for about \$90 (don’t buy it from a college bookstore…you’ll pay full price, \$150+!).

Why should you buy a TI-89 Calculator for your elementary statistics course? Here is an example of how easy the TI-89 makes statistics:

Variance and Standard Deviation problems are perhaps the most basic problems elementary statistics students are taught. They are taught in the first couple days of any statistics course. Here’s the difference between calculating variance and standard deviation manually, versus using the TI-89:

Find the variance and standard deviation of 12, 48, 79, 99, 101.

## Manually

Step 1: Add the numbers in the list.
12 + 48 + 79 + 99 + 101 = 339

Step 2: Square the sum, and divide by the number of items in the data set:
339 × 339 = 114,921
114,921 / 5 = 22,984.2

Step 3: Take your original numbers from step 1, square them individually, and add them up:
(12 × 12) + (48 × 48) + (79 × 79) + (99 × 99) + (101 × 101) = 28,691

Are you getting bored yet?

Step 4: Subtract the amount in step 2 from the amount in step 3:
28,691 – 22,984.2 = 5,706.799999999999

Step 5: Subtract 1 from the number of items in my data set:
5 – 1 = 4

Step 6: Divide by the number in step 4 by the number in step 5:
5,706.799999999999 / 4 = 1,426.6999999999998

That’s the Variance.

Step 7: Take the square root of the number from step 6.
√(1,426.6999999999998) = 37.77168251481525

That’s the Standard Deviation.

## Using the TI-89

Step 1: Enter the list of numbers.

Step 2: Select the Variance or Standard Deviation functions, depending on which you want.

Step 3: Yawn and stretch. There is no step 3! You’re done!

Still not convinced that the TI-89 will save you time and stress?

Let’s look at how the calculator can help you with a more complex problem, like Linear Regression. The calculation for Linear Regression will take you 15 to 30 minutes depending on how confident you are with your math skills. You can find a linear equation on a TI-89 in less than a minute!

Here are the methods, side by side:

## Manual Linear Regression

Step 1: Make a chart of your data, filling in the columns in the same way as you would fill in the chart if you were finding the Pearson’s Correlation Coefficient.

Subject Age x Glucose Level y xy x2 y2
1 43 99 4257 1849 9801
2 21 65 1365 441 4225
3 25 79 1975 625 6241
4 42 75 3150 1764 5625
5 57 87 4959 3249 7569
6 59 81 4779 3481 6561
Σ 247 486 20485 11409 40022

From the above table, Σx = 247, Σy = 486, Σxy = 20485, Σx2 = 11409, Σy2 = 40022. n is the sample size (6, in our case).

Step 2. Use the following equations to find a and b.

Find a:

• ((486 × 11,409) – ((247 × 20,485)) / 6 (11,409) – 2472)
• 5,544,774 – (5,059,795 / 7,445)
• =553,794

Find b:

• (6(20,485) – (247 × 486)) / (6 (11409) – 2472)
• (122,910 – 120,042) / 68,454 – 2472
• 2,868 / 7,445
• = .385225

Step 3: Insert the values into the equation.
y’ = a + bx
y’ = 553,794 + .385225x

## TI-89 Linear Regression

Step 1: Enter the X and Y values into the TI-89.

Step 2: Select the Linear Regression Function from the menu.

Expecting more? Sorry to disappoint: you’re done.

Think about how much exam time the TI-89 will save you!

Now, I have built online calculators for a couple of common statistics calculations, but no online calculator can compare with the hundreds of functions available in the TI-89. Plus, you aren’t typically allowed to use online resources during an exam (and even if you are, what happens if the internet goes down?).

Do yourself a favor: save your time and energy. Go to Amazon, buy the TI-89, you won’t be sorry.

Buy the TI-89 from Amazon.com Now →