ACT Math : How to evaluate algebraic expressions

Study concepts, example questions & explanations for ACT Math

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Example Questions

Example Question #11 : Evaluating Expressions

What is the value of x that satisfies the equation 5(x+2)=12x-5 ?

Possible Answers:

-\frac{15}{17}

1

0

\frac{15}{7}

\frac{15}{11}

Correct answer:

\frac{15}{7}

Explanation:

Distributing the 5 on the left side of the equation gives you 5x+10=12x-5.

Subtracting 5x from both sides of the equation gives you 10=7x-5.

Adding 5 to both sides of the equation gives you 15=7x.

Dividing each side of the equation by 7 gives you \frac{15}{7}=x.

Example Question #11 : Evaluating Expressions

If \small a = 2 and \small b = 4 , what is \small -4(ab)^{3} + (3a - 2b)?

Possible Answers:

-2050

-2046

-32,770

2046

2050

Correct answer:

-2050

Explanation:

\small -4(2\times 4)^{3} + \left ( 3\times 2 - 2\times 4 \right )

\small -4(512) + (6-8)

\small -2048 -2

\small -2050

Example Question #12 : Evaluating Expressions

8 less than 4 times a number is 76. Find the number.

Possible Answers:

Correct answer:

Explanation:

Example Question #11 : Evaluating Expressions

Let and .  Solve zx^{y}

Possible Answers:

Correct answer:

Explanation:

Substitute the given values into the variables to get:

4(2^{3})= 4(8)= 32

Example Question #15 : Evaluating Expressions

Bob needs to order  candy bars from a warehouse. The website he is ordering from shows that the candy bars come in cases of  boxes with candy bars in each box. It is not possible to order partial cases. What is the fewest amount of cases that Bob should order?

Possible Answers:

Correct answer:

Explanation:

The answer is .

Bob must order full cases, which contain  boxes of candy bars with  bars per box. This comes out to a total of  candy bars per case. An order of  cases comes out to  candy bars which is not enough. However if he orders one more case, the total comes out to  candy bars which allows him to barely surpass his needed amount of  bars.

Example Question #11 : How To Evaluate Algebraic Expressions

Solve for :

Possible Answers:

Correct answer:

Explanation:

The answer is .

To solve this equation for , first distribute the  to make the equation

. Next, subtract from both sides to leave you with . Finally, divide both sides by  to determine that .

Example Question #17 : Evaluating Expressions

If three chairs cost , what is the cost of chairs?

Possible Answers:

Correct answer:

Explanation:

The answer is .

If three chairs cost , each chair costs . To determine the cost of two chairs, multiply .

Example Question #11 : How To Evaluate Algebraic Expressions

Evaluate the expression  for 

Possible Answers:

Correct answer:

Explanation:

The answer is 

To solve this expression subsitute  for . This results in . Simplify to get  as the answer.

Example Question #19 : Evaluating Expressions

If 40% of  equals 8, then 

Possible Answers:

Correct answer:

Explanation:

The equation can be set up as follows:

Solve for 

Now that we know the value of , we can plug it in to our final equation:

Remember, in this scenario, we must follow proper order of operations, where power is taken in consideration before multiplication.

In other words, 20 is squared first, giving 400. 

In our last step, we multiple 400 by 0.5, giving our final answer: 200

*Note, the other answer choices generally consist of answers at other steps of the problem or answers arrived at when not following proper order of operations. Be careful when answering questions like these, as they often have other answer choices meant to catch your mistake on the ACT.

Example Question #20 : Evaluating Expressions

If , then what is

?

Possible Answers:

Correct answer:

Explanation:

One can arrive to the answer two ways. They can either use FOIL then plug in  for or they can plug in  for  first, and then solve.

We recommend using the latter approach, as it saves more time, an important skill to recognize to be successful on the ACT.

By plugging in  for , we have:

Which simplifies to,

 or 

 

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