»

# TI 8xx Series by Christopher Monahan

Five volunteers are asked to read this tongue twister: How many boards could the Mongols hoard if the Mongol horde got bored?

The volunteers are numbered 1 through 5. Volunteer 1 reads the tongue twister, and the time needed to read the tongue twister, as measured with a stopwatch, is recorded. The watch is reset, and volunteer 1 again reads the tongue twister, with the difference that volunteer 2 will begin reading the tongue twister when volunteer 1 has finished. When the second person has finished reading, the data are recorded on the second line. This process is extended to the third volunteer, then to the fourth, and finally to the fifth. The data in the table represent the number of people who read (column L1) and the time, in seconds (column L2).

Press STAT, option 1: Edit and enter the data.

Before creating the scatter plot for the data, go to the equation editor (Y=) and either turn it off (put the cursor on the equals sign, and press ENTER so that the equals sign is no longer back-lit) or clear any active equations. Press 2nd Y= to go to the STAT PLOT menu. Press ENTER for Plot 1. With the cursor on the ON option, press ENTER.

Press the ZOOM button, and choose option 9:ZSTAT to have the calculator determine the window for the scatter plot. You can always adjust the window through the WINDOW button.

It looks like a line will pass through these points. A linear regression is a good option.

The calculator contains a diagnostic command that will return the values of the correlation coefficient, r, and the coefficient of determination, r2. Turn this on by pressing 2nd 0 to go to the Catalog, x-1 to go to the D's. Scroll down until you reach the Diagnostic On command.

Have the calculator determine the line of best fit by pressing the STAT button, right arrow to the CALC menu, and choose option 4: LinReg(ax+b).

The calculator requires two pieces of information for the LinReg command: the list containing the input values and the list containing the output values. You have the option of including the location where you would like the equation stored. Before proceeding, take a moment to look at your calculator. Above the numbers 1–6 you will find L1–L6 on the calculator plate. These are the six default lists that come with the calculator.

1. Press 2nd 1 to select L1 as the input list.

2. The input list and output list must be separated by a comma, which you will find on the row above the 7.

3. Press 2nd 2 to select L2 as the output values.

4. Put a comma after L2 and enter the location of the equation in which you would like to store the data.

5. To the left of the CLEAR button is the VARS button. Press this button and the right arrow to activate the Y-VARS menu. Choose option 1: Functions. You have access to the ten Y1–Y0 that come with the calculator. Choose one of these.

Press ENTER to complete the regression.

Press GRAPH to see how well this equation fits the data.

The slope of the regression line is 3.243. The number is interpreted to mean that it takes an average of 3.243 seconds for the tongue twister to be read. The value of the vertical intercept—the time needed for 0 people to read the tongue twister—has no pertinent meaning in this case.

Read More Regression with Graphing Calculators
Shopping

#### THE EVERYTHING GUIDE TO ALGEBRA

By Christopher Monahan

1. Home
2. Algebra
3. Regression with Graphing Calculators
4. TI 8xx Series