ACT Math : Equations / Inequalities

Study concepts, example questions & explanations for ACT Math

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Example Questions

Example Question #201 : Equations / Inequalities

Given the follow inequality, which of the following presents a range of possible answers for the inequality: –3 < 3x + 2 ≤ 3.5

Possible Answers:

(–1, ½)

( –2, 2)

(½, 1)

(–1,1)

(–3, 1/2)

Correct answer:

(–1, ½)

Explanation:

If you plug in the outer limits of the given ranges, (–1, ½) is the only combination that fits within the given equation. It is important to remember that "<" means “less than,” and "≤" means “less than or equal.” For example, if you answered (–2,2), plugging in 2 would make the the expression equal 8, which is greater than 3.5. And plugging in –2 for x would make the expression equal –4, which is less than –3, not greater. However, plugging in the correct answer (–1, ½) gives you –1 as your lower limit and 3.5 as your upper limit, which satisfies the equation. Both limits of the data set must satisfy the equation. 

Example Question #202 : Equations / Inequalities

If , what is the product of the largest and smallest integers that satisfy the inequality?

Possible Answers:

0

–5

7

5

–10

Correct answer:

0

Explanation:

The inequality in the question possesses an absolute value; therefore, we most solve for the variable being less than positive 6 and greater than negative 6. Let's start with the positive solution.

 

Add 4 to both sides of the inequality.

Divide both sides of the inequality by 2.

Now, let's solve for the negative solution

Add 4 to both sides of the inequality.

Divide both sides of the inequality by 2.

Using these solutions we can write the following statement: 

The smallest integer that satisfies this equation is 0, and the largest is 4. Their product is 0. 

Example Question #201 : Equations / Inequalities

Solve 8x2 – 2x – 15 = 0

Possible Answers:

x = 3/2 or 5/4

x = 3/2 or -5/4

x = -3/2 or 5/4

x = -3/2 or -5/4

Correct answer:

x = 3/2 or -5/4

Explanation:

The equation is in standard form, so a = 8, b = -2, and c = -15.  We are looking for two factors that multiply to ac or -120 and add to b or -2.  The two factors are -12 and 10.

So you get (2x -3)(4x +5) = 0.  Set each factor equal to zero and solve.

 

 

Example Question #202 : Equations / Inequalities

If (x+ 2) / 2 = (x2 - 6x - 1) / 5, then what is the value of x?

Possible Answers:

4

3

2

-3

-2

Correct answer:

-2

Explanation:

(x+ 2) / 2 = (x2 - 6x - 1) / 5. We first cross-multiply to get rid of the denominators on both sides.

5(x2 + 2) = 2(x2 - 6x - 1)

5x2 + 10 = 2x2 - 12x - 2 (Subtract 2x2, and add 12x and 2 to both sides.)

3x2 + 12x + 12 = 0 (Factor out 3 from the left side of the equation.)

3(x2 + 4x + 4) = 0 (Factor the equation, knowing that 2 + 2 = 4 and 2*2 = 4.)

3(x + 2)(x + 2) = 0

x + 2 = 0

x = -2

 

Example Question #203 : Equations / Inequalities

Which of the following is a factor of the polynomial x2 – 6x + 5?

Possible Answers:

x + 2

x – 5

x – 8

x – 6

x + 1

Correct answer:

x – 5

Explanation:

Factor the polynomial by choosing values that when FOIL'ed will add to equal the middle coefficient, 3, and multiply to equal the constant, 1.

x2 – 6+ 5 = (x – 1)(x – 5)

Because only (x – 5) is one of the choices listed, we choose it.

Example Question #204 : Equations / Inequalities

7 times a number is 30 less than that same number squared. What is one possible value of the number?

Possible Answers:

-10

0

3

1

-3

Correct answer:

-3

Explanation:

\small 7x+30=x^{2}

\small x^{2}-7x-30=0

\small (x-10)(x+3)=0

Either:

\small x-10=0

\small x=10

or:

\small x+3=0

\small x=-3

Example Question #205 : Equations / Inequalities

Which of the following is equivalent to ?

Possible Answers:

Correct answer:

Explanation:

The answer is .

To determine the answer,  must be distrbuted,

. After multiplying the terms, the expression simplifies to .

Example Question #206 : Equations / Inequalities

For what value of b is the equation b2 + 6b + 9 = 0 true?

Possible Answers:

3

0

5

3

Correct answer:

3

Explanation:

Factoring leads to (b+3)(b+3)=0. Therefore, solving for b leads to -3.

Example Question #207 : Equations / Inequalities

What is the solution to:

 

Possible Answers:

2

1

4

0

6

Correct answer:

4

Explanation:

First you want to factor the numerator from x– 6x + 8 to (x – 4)(x – 2)

Input the denominator (x – 4)(x – 2)/(x – 2) = (x – 4) = 0, so x = 4.

 

Example Question #208 : Equations / Inequalities

What is the value of  where:

Possible Answers:

Correct answer:

Explanation:

The question asks us to find the value of , because it is in a closed equation, we can simply put all of the whole numbers on one side of the equation, and all of the  containing numbers on the other side.

 

We utilize opposite operations to both sides by adding  to each side of the equation and get 

 

Next, we subtract  from both sides, yielding

 

 

Then we divide both sides by  to get rid of that  on 

 

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