Okay, so apologies if I touch on stuff you've already done, but I'm going to go through it step by step. :)

First thing you do is put your points in, so you press the yellow

2ND and then press the blue

Y= button (since you hit

2ND, you're actually pressing

STAT PLOT). This will bring up a menu of your plots: Plot 1, Plot 2, Plot 3... For now, you will only need Plot 1, so make sure the cursor is highlighting

1: and hit

ENTER. That will bring you to the plot setup screen, that looks like this:

Make sure your cursor highlights the On field and hit

ENTER again. This tell the calculator to pay attention to Plot 1. You'll also want to make sure your calculator is set to make it a scatter plot (bunch of dots) and not a line, so next to where it says Type: make sure the top left option is selected - the one that looks like a bunch of dots.

Yours will be a little different from this, in that it will say Xlist: L1 and Ylist: L2. That means that you're using List 1 as your X values and List 2 as your Y values. Let's go and fill those in now. Press

2ND and

MODE on your calculator (which really is telling the calculator to

QUIT out of that screen).

Now you want to press

STAT, which is located near the left arrow in the middle right hand of the keypad. The TI-83 plus has EDIT as the default option under STAT, so just go ahead and hit

ENTER again since you want to edit your lists. After you do that, you will see a screen that looks like this:

If you have values in your L1 or L2 columns, clear them out by highlighting the L# at the top of the list, hitting

CLEAR, and then pressing the

DOWN ARROW. Once all of your lists are clear, you can start entering your data.

Remember that your L1 list is your X values, so you want to enter the X values of all your points (0, 10, 20, 26, 28) in L1. Then go and enter all your Y values under L2 (so it'll be 38, 37, 36, 36.3, 36.4). After that's done, you want to hit

Y= and clear out anything in there so that you have no other data interfering in your scatter plot. Then hit

GRAPH.

Now, when I did this, my calculator was set on the standard window, which goes from -10 to 10 on both the X and Y axes. Since your data set is outside that range, you might have to change the focus on your graph to be able to see the scatter plot. You can do this by pressing the

WINDOW button. Then set your X range to be just outside your data range. You probably want it to be Xmin = -5 and Xmax = 30. If you really want to, you can change Xscl to equal 5, but it doesn't really matter for this particular exercise. Then change Ymin to 30 and Ymax to 40 (since all your Y values are between 30 and 40). Then press

GRAPH again to see your nice scatter plot.

To find the line of best fit, perform a linear regression on L1 and L2. This is done by quitting out of your graph (remember you press

2ND and

MODE in order to get

QUIT) and then pressing

STAT and selecting CALC with the

RIGHT ARROW key and then

ENTER. When you do a regression, you have to tell the calculator what to use. Remember that coordinates go in X,Y format, and the regression function goes in the same order. So after pressing

STAT, selecting CALC, and pressing the number

4 (for a linear regression), your screen will say LinReg(ax+b) and then have a blinking cursor. You can press

2ND and number

1 (which will fill in L1), then hit the

comma key (above the number

7) to separate the sets of coordinates. Press

2ND and the number

2 to fill in your Y values. Don't hit enter yet! You can use the regression function to plug the regressed function right into your Y= screen by doing this:

- Press the

comma key again.

- Press

VARS (short for variables)

- Select Y-VARS with the

RIGHT ARROW, then press the number

1 (for Function).

- Select which Y= line you want your equation to go to. If you already have something filled into the top Y= line (which you can check by pressing

Y=), you might find it useful to press the number

2 and have it fill in the regression in the second Y= line. For the purposes of what we have so far, though, you're going to press

1 right now.

So now your screen should say LinReg(ax+b) L1,L2,Y1. Hit enter. You'll see your regression results pop up. You can look at them in more detail, and you can view your best-fit line by hitting

GRAPH again. Try doing a quadratic or cubic regression next and see if those fit your line any better. :)