Evaluating Expression

Lesson Objective

Learn how to evaluate expressions by substituting variables and perform the required calculations.

About This Lesson

From the lesson algebra variables, you know that a variable is used to represent a certain number.

Therefore, you can evaluate an expression by substituting the each variable in the expression with its given number and perform the required calculations. This lesson shows you how.

Study Tips

Tip #1

Remember to include brackets around the substituted variable. These brackets help to minimize calculation mistakes.

Tip #2

It is better to substitute the variables in the expression one at a time. You can substitute the variables all at once when you are more familiarized with the steps involved.

Now, watch the following math video to know more.

Math Video

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Math Video Transcript

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In the lesson ' Algebra Variables',  we learn that variable can be used to represent a certain  number.  

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Therefore,  we can evaluate an algebraic expression by substituting each variable with a given number and perform the required calculation. 

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This lesson shows you how.

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Let's evaluate the expression when p =3, and r = -2.

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For this expression, only variable p is present. So, substituting p with 3. 

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Remember to always put brackets around the substituted number. This is to minimize mistakes.

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Now, multiply 2 with 3. this gives 6. next, Add 6 with 2. This gives 8 . Therefore, The evaluated expression is 8. 

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Now, let's evaluate 4p + 3r. We can start by substituting p with 3. 

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Next, multiply 4 with 3. This gives 12. 

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Now, substitute r = -2.  multiply  3 with -2. This gives -6.

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Minus 12 with 6. This gives the answer 6.

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Next example,   p the power of 3,  minus 2r square, minus 2.  

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Let's start by substituting r with  -2. Now, -2 square is equals to -2 multiply by  -2, which is equals to 4. 

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Next, we multiply  -2 with 4. This gives -8. 

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Now, by adding -8  and  -2, we get -10. 

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Let's substitute p with 3. Now, 3 power of 3 is equals to, 3 * 3 * 3. This gives 27.

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Alright,  the final answer is 27  minus 10, which is  17.

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One final example, let's evaluate r square minus 2pr. Substituting r with  negative 2.

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Now, negative two to the power of 2 is equals to, -2 multiply by  -2. This gives 4.

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Let's substitute p with 3. -2 multiply by 3 gives negative 6.

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Now, substitute r with  -2.

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Multiply -6 with -2 gives +12.

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Now add 4 with +12. The answer is 16.

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Alright, that's all for this lesson. Try out the practice questions to  better  your understanding.

Practice Questions & More

Multiple Choice Questions (MCQ)

Now, let's try some MCQ questions to understand this lesson better.

You can start by going through the series of questions on evaluating expression or pick your choice of question below.

Question 1 on the basics
Question 2 on the basics

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