Before you toss coins, roll dice, pick marbles, spin spinners, or draw cards, you need to know how to access the commands at the bottom of the TI-84 Plus Probability Simulation screen, how to seed the random number generator, and what the ESC command does.

## How to execute commands in Probability Simulation

At the bottom of each screen, you see a line of five boxes containing from two to five commands, as illustrated in the second image where the boxes contain four commands (OK, OPTN, ABOUT, and QUIT) with no command in the second box.

Under these boxes are five calculator keys: [Y=], [WINDOW], [ZOOM], [TRACE], and [GRAPH]. You execute the command by pressing the calculator key that is under the box. For example, in the second image, the OPTN command is executed by pressing [ZOOM].

## How to seed the random number generator in Probability Simulation

The calculator doesn’t really generate random numbers; it uses a formula to generate a sequence of numbers that appear to be random. Each number in this sequence is dependent on the number that precedes it. Thus the whole sequence is determined by the first number in the sequence.

This number is called the seed; assigning a value to the seed is called seeding the random number generator. If you seed two different TI-84’s with the same number, the random number generator will produce the same sequence of numbers on each calculator. Now that isn’t very random, is it?

The outcome of each simulation performed by the Probability Simulation application, whether it be tossing a coin or spinning a spinner, is determined by a random number generated by Probability Simulation’s random number generator. Usually, you don’t need to seed the random number generator to ensure that you get a “random” outcome.

You can just accept whatever number the calculator uses as a seed because it uses the last random number it generated as the seed.

However, if you want to ensure that a simulation is replicated on two or more TI-84’s, set the seed to the same number on each calculator. Or if you want to ensure that a simulation is not replicated, set the seed to a random number of your choice.

To seed the random number generator, follow these steps:

1. Go to Probability Simulation’s Main menu.

The Main menu is the first screen you see when you start the Probability Simulation application. If you are not in the Main menu, repeatedly press [Y=] until this menu appears.

2. Press [ZOOM] to execute the OPTN command.

A blinking cursor appears, waiting for you to enter a number.

3. Use the keypad to enter any positive integer.

4. Press [GRAPH] to select the OK option.

The random number generator is seeded by the number you entered, and you are returned to the Main menu.

## Go back to the previous screen in Probability Simulator

The ESC command sends you back to the previous screen. If it is available, it is always the first command in the command line at the bottom of the screen. So it is always executed by pressing [Y=].