# Replacing Variables with Plug-in Method on TI-30 XS

In this lesson, we’ll explain how to replace variables, also with the plug-in method, to solve Math problems with the GED calculator TI-30 XS. This lesson is included in our free online GED® classes.

In the second part of the GED Math exam, you can use a scientific calculator but it has to be the TI-30 XS.

If you understand how to use this scientific calculator effectively, you will definitely reach a passing score on GED Math!

Our free online GED classes are a perfect tool for GED students, especially those with busy lives looking to get better and better-paying jobs.

In some Math questions, letters stand for numbers. These letters represent unknown values and are called variables.

When we replace letters with a given number, we can perform the usual Math operations. This process is known as evaluating expressions.

Here is a simple example.

Calculate:

1/2a+33

when a=184.

Is it: Option one: 125?

Or Option two: 97?

So, you need to replace the letter “a” with the number 184 and then calculate the total value.
So, we need to input the following expression:
½ times 184 plus 33.

Let us use our TI 30XS to perform this calculation.

Press the fraction sign and type 1 in the upper box, then use the arrow to navigate to the lower box and press 2. Press enter to finish editing this fraction. Our screen shows the ½ fraction, now press the multiplication sign and then type 184. Then punch the plus sign for addition and type 33, and finally press the enter sign to see the result.
It’s 125.

So, option 1 is correct.

Step-By-Step Explanation

Replacing Variables Plug-in Method

Some questions ask you to replace two or more variables.

Then, the plug-in method is more convenient. In this method, you program our TI 30 XS, to replace variables and perform operations.

We will use two new buttons to help us with this task.

First, look at this key that says S T O, this key is used to store given values in the memory of the calculator. The second button we will use has a big x and a bunch of smaller letters. This key, in combination with the STO key, assigns a given value to a letter.

Let’s see how it works.
evaluate 2x + 5y minus z.
At x = 3, y = 13, z= negative 6.

Is it Option one:  182? Or Option two: 77?

Step-By-Step Explanation

1. Evaluate the expression at the given value of $$x$$ and $$y$$.

$$-3x - 6y + 3$$,

at  $$x = 8$$,

$$y = 7$$
A.
B.
C.
D.

Question 1 of 3

2. Evaluate.

$$12x^{2} + \frac{1}{4} y - 6z$$

at  $$x = 2$$,

$$y = 8$$,

$$z = -7$$,

Tip. Make sure, you have input $$\frac{1}{4} y$$ correctly.
A.
B.
C.
D.

Question 2 of 3

3. Evaluate.

$$3x + 12y$$,

at $$x = -7$$.

$$y = \frac{3}{4}$$.
A.
B.
C.
D.

Question 3 of 3

First, we want to program our calculator, so it remembers that x = 3, y=13, and z = negative 6. Here is how to do it. Press 3 and now click the S T O key.
Now you need to assign a letter x to 3,

Click this button that has a big x and a bunch of smaller letters.
Look at the screen. It shows the number 3, and the arrow points towards the letter x.
It means that our calculator assigns x to the number 3.

Let’s continue. Type 13 and press the S T O button, to store this number.

Now press this button with the x and a bunch of letters. The first letter, you will see on the screen is x.

Press this button again and you will see a letter y. Press enter to confirm this choice. When you look at the screen, you will see 13 pointing the arrow towards the letter y. That’s good. Now, let repeat the same process, to assign negative 6 to the letter z.

So, we programmed our calculator and now it will replace letters x, y, and z, with 3, 13, and negative 6. Now, it’s time to input our expression. 2x + 5y minus z. Type 2 and then click the key with one big x and a bunch of letters.
The screen shows the letter x next to the number 2.

So, we now have 2x.
Now, type the plus sign for addition and press 5.

Press the button with x and a bunch of letters. You will see a letter x, press again and there will be a letter y. Press the subtraction key and press the key with x and a bunch of letters, to input z. You need to press this button 3 times to input z. Your screen should display our expression2x + 5y minus z.

Press enter for the result. It’s 77.

Our TI 30 XS replaced variables with stored numbers and performed the calculation. So, now you know how to use the plug-in method.

This is a very useful method that you can use for evaluation functions and solving linear equations and as well as solving inequalities.

To continue learning about more possibilities of using the TI-30 XS for solving Math problems, check the Covcel website.

So this was our explanation about replacing variables and replacing variables with the plug-in method. This lesson is part of our Calculator Series of our free online GED classes to help students pass the Math portion by learning how to work with the TI-30 XS calculator.

Check out also our other free online GED classes that cover the academic fields that the four GED modules relate to: Social Studies, Language Arts, Math, and Science.

Last Updated on April 6, 2021.