PSAT Math : Inequalities

Study concepts, example questions & explanations for PSAT Math

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Example Questions

Example Question #131 : Equations / Inequalities

If –1 < w < 1, all of the following must also be greater than –1 and less than 1 EXCEPT for which choice?

Possible Answers:

|w|

w2

w/2

3w/2

|w|0.5

Correct answer:

3w/2

Explanation:

3w/2 will become greater than 1 as soon as w is greater than two thirds. It will likewise become less than –1 as soon as w is less than negative two thirds. All the other options always return values between –1 and 1.

Example Question #21 : Inequalities

Solve for \(\displaystyle z\).

\(\displaystyle \left | z-3 \right |\geq 5\)

Possible Answers:

\(\displaystyle z\leq -2\ \text{or}\ z\geq 8\)

\(\displaystyle z\geq 8\)

\(\displaystyle -3\leq z\leq 5\)

\(\displaystyle z\leq -3\ \text{or}\ z\geq 5\)

\(\displaystyle -2\leq z\leq 8\)

Correct answer:

\(\displaystyle z\leq -2\ \text{or}\ z\geq 8\)

Explanation:

Absolute value problems always have two sides: one positive and one negative.

First, take the problem as is and drop the absolute value signs for the positive side: z – 3 ≥ 5. When the original inequality is multiplied by –1 we get z – 3 ≤ –5.

Solve each inequality separately to get z ≤ –2 or z ≥ 8 (the inequality sign flips when multiplying or dividing by a negative number).

We can verify the solution by substituting in 0 for z to see if we get a true or false statement. Since –3 ≥ 5 is always false we know we want the two outside inequalities, rather than their intersection.

Example Question #256 : New Sat

If x+1< 4\(\displaystyle x+1< 4\) and y-2<-1\(\displaystyle y-2< -1\) , then which of the following could be the value of \(\displaystyle x+y\)?

Possible Answers:

\(\displaystyle 16\)

\(\displaystyle 12\)

\(\displaystyle 4\)

\(\displaystyle 0\)

\(\displaystyle 8\)

Correct answer:

\(\displaystyle 0\)

Explanation:

To solve this problem, add the two equations together:

x+1<4\(\displaystyle x+1< 4\)

y-2<-1\(\displaystyle y-2< -1\)

x+1+y-2<4-1\(\displaystyle x+1+y-2< 4-1\)

x+y-1<3\(\displaystyle x+y-1< 3\)

x+y<4\(\displaystyle x+y< 4\)

The only answer choice that satisfies this equation is 0, because 0 is less than 4.

Example Question #1 : How To Find The Solution To An Inequality With Addition

If \(\displaystyle 17-x>19\), which of the following could be a value of \(\displaystyle x\)?

Possible Answers:

-\(\displaystyle -2\)

\(\displaystyle 4\)

\(\displaystyle 2\)

\(\displaystyle 0\)

\(\displaystyle -4\)

Correct answer:

\(\displaystyle -4\)

Explanation:

In order to solve this inequality, you must isolate \(\displaystyle x\) on one side of the equation. 

\(\displaystyle 17-x>19\)

\(\displaystyle 17 > 19 +x\)

\(\displaystyle -2 > x\)

Therefore, the only option that solves the inequality is \(\displaystyle -4\)

 

Example Question #22 : Inequalities

What values of \(\displaystyle x\) make the statement \(\displaystyle \left |5x-9 \right |\geq6\) true?

Possible Answers:

\(\displaystyle x\geq5,x\leq \frac{1}{5}\)

\(\displaystyle x\geq15,x\leq \frac{2}{5}\)

\(\displaystyle x\geq3, x\leq \frac{3}{5}\)

\(\displaystyle x\geq6,x\leq \frac{1}{3}\)

\(\displaystyle x\geq4,x\leq -\frac{1}{2}\)

Correct answer:

\(\displaystyle x\geq3, x\leq \frac{3}{5}\)

Explanation:

First, solve the inequality \(\displaystyle 5x-9 \geq6\):

\(\displaystyle 5x-9 \geq6\)

\(\displaystyle 5x\geq15\)

\(\displaystyle x\geq3\)

Since we are dealing with absolute value, \(\displaystyle 5x-9\leq-6\) must also be true; therefore:

\(\displaystyle 5x-9\leq-6\)

\(\displaystyle 5x\leq3\)

\(\displaystyle x\leq \frac{3}{5}\)

Example Question #151 : Algebra

If –1 < n < 1, all of the following could be true EXCEPT:

Possible Answers:

(n-1)2 > n

16n2 - 1 = 0

n2 < n

n2 < 2n

|n2 - 1| > 1

Correct answer:

|n2 - 1| > 1

Explanation:

N_part_1

N_part_2

N_part_3

N_part_4

N_part_5

Example Question #166 : Equations / Inequalities

(√(8) / -x ) <  2. Which of the following values could be x?

Possible Answers:

-1

-3

-2

-4

All of the answers choices are valid.

Correct answer:

-1

Explanation:

The equation simplifies to x > -1.41. -1 is the answer.

Example Question #31 : Inequalities

Solve for x

\small 3x+7 \geq -2x+4\(\displaystyle \small 3x+7 \geq -2x+4\)

 

Possible Answers:

\small x \geq -\frac{3}{5}\(\displaystyle \small x \geq -\frac{3}{5}\)

\small x \leq \frac{3}{5}\(\displaystyle \small x \leq \frac{3}{5}\)

\small x \geq \frac{3}{5}\(\displaystyle \small x \geq \frac{3}{5}\)

\small x \leq -\frac{3}{5}\(\displaystyle \small x \leq -\frac{3}{5}\)

Correct answer:

\small x \geq -\frac{3}{5}\(\displaystyle \small x \geq -\frac{3}{5}\)

Explanation:

\small 3x+7 \geq -2x+4\(\displaystyle \small 3x+7 \geq -2x+4\)

\small 3x \geq -2x-3\(\displaystyle \small 3x \geq -2x-3\)

\small 5x \geq -3\(\displaystyle \small 5x \geq -3\)

\small x\geq -\frac{3}{5}\(\displaystyle \small x\geq -\frac{3}{5}\)

Example Question #151 : Algebra

We have \(\displaystyle x^2-4< 0\), find the solution set for this inequality. 

Possible Answers:

\(\displaystyle x>-2\)

\(\displaystyle x< 2\)

\(\displaystyle -2< x< 2\)

\(\displaystyle x=0\)

\(\displaystyle x>2, x< -2\)

Correct answer:

\(\displaystyle -2< x< 2\)

Explanation:

\(\displaystyle x^2-4< 0 \Rightarrow x^2< 4 \Rightarrow -2< x< 2\)

Example Question #32 : Inequalities

Fill in the circle with either <\(\displaystyle < \), >\(\displaystyle >\), or =\(\displaystyle =\) symbols:

(x-3)\circ\frac{x^2-9}{x+3}\(\displaystyle (x-3)\circ\frac{x^2-9}{x+3}\) for x\geq 3\(\displaystyle x\geq 3\).

 

Possible Answers:

The rational expression is undefined.

(x-3)=\frac{x^2-9}{x+3}\(\displaystyle (x-3)=\frac{x^2-9}{x+3}\)

None of the other answers are correct.

(x-3)> \frac{x^2-9}{x+3}\(\displaystyle (x-3)> \frac{x^2-9}{x+3}\)

(x-3)< \frac{x^2-9}{x+3}\(\displaystyle (x-3)< \frac{x^2-9}{x+3}\)

Correct answer:

(x-3)=\frac{x^2-9}{x+3}\(\displaystyle (x-3)=\frac{x^2-9}{x+3}\)

Explanation:

(x-3)\circ\frac{x^2-9}{x+3}\(\displaystyle (x-3)\circ\frac{x^2-9}{x+3}\)

Let us simplify the second expression. We know that:

(x^2-9)=(x+3)(x-3)\(\displaystyle (x^2-9)=(x+3)(x-3)\)

So we can cancel out as follows:

\frac{x^2-9}{x+3}=\frac{(x+3)(x-3)}{(x+3)}=x-3\(\displaystyle \frac{x^2-9}{x+3}=\frac{(x+3)(x-3)}{(x+3)}=x-3\)

(x-3)=\frac{x^2-9}{x+3}\(\displaystyle (x-3)=\frac{x^2-9}{x+3}\)

 

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