SAT Math : How to find the solution to an inequality with addition

Study concepts, example questions & explanations for SAT Math

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Example Questions

Example Question #3 : Inequalities

What values of x make the following statement true?

|x – 3| < 9

Possible Answers:

6 < x < 12

–12 < x < 6

x < 12

–3 < x < 9

–6 < x < 12

Correct answer:

–6 < x < 12

Explanation:

Solve the inequality by adding 3 to both sides to get x < 12.  Since it is absolute value, x – 3 > –9 must also be solved by adding 3 to both sides so: x > –6 so combined.

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

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

Possible Answers:

w2

|w|0.5

3w/2

w/2

|w|

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 #2 : How To Find The Solution To An Inequality With Addition

Solve for \(\displaystyle z\).

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

Possible Answers:

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

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

\(\displaystyle z\geq 8\)

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

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

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 #233 : Gre Quantitative Reasoning

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

Possible Answers:

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

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

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

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

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

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

Solve:  \(\displaystyle 3x+2\le 49\)

Possible Answers:

\(\displaystyle x\le \frac{17}{3}\)

\(\displaystyle x\le \frac{47}{3}\)

\(\displaystyle x\ge \frac{47}{3}\)

\(\displaystyle x\le 17\)

\(\displaystyle x\le 47\)

Correct answer:

\(\displaystyle x\le \frac{47}{3}\)

Explanation:

To solve \(\displaystyle 3x+2\le 49\), isolate \(\displaystyle x\).

\(\displaystyle 3x\le 47\)

Divide by three on both sides.

\(\displaystyle x\le \frac{47}{3}\)

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

Solve for \(\displaystyle x\).

\(\displaystyle -5x+17>62\)

Possible Answers:

\(\displaystyle x>-9\)

\(\displaystyle x=-9\)

\(\displaystyle x\leq-9\)

\(\displaystyle x< -9\)

\(\displaystyle x\geq-9\)

Correct answer:

\(\displaystyle x< -9\)

Explanation:

We want to isolate the variable on one side and numbers on another side. Treat like a normal equation. 

\(\displaystyle -5x+17>62\) Subtract \(\displaystyle 17\) on both sides.

\(\displaystyle -5x>45\) Divide \(\displaystyle -5\) on both sides. Remember to flip the sign.

\(\displaystyle x< -9\)

Example Question #22 : Inequalities

Solve for \(\displaystyle x\).

\(\displaystyle 4x+7< 5x+13\)

Possible Answers:

\(\displaystyle x\geq-6\)

\(\displaystyle x=-6\)

\(\displaystyle x< -6\)

\(\displaystyle x\leq-6\)

\(\displaystyle x>-6\)

Correct answer:

\(\displaystyle x>-6\)

Explanation:

We want to isolate the variable on one side and numbers on another side. Treat like a normal equation. 

\(\displaystyle 4x+7< 5x+13\) Subtract \(\displaystyle 4x,13\) on both sides.

\(\displaystyle x< -6\)

Example Question #6 : How To Find The Solution To An Inequality With Addition

Solve for \(\displaystyle x\).

\(\displaystyle \left | x+5\right |< 8\)

Possible Answers:

\(\displaystyle x=3, x=-13\)

\(\displaystyle x>3, x< -13\)

\(\displaystyle x>3\)

\(\displaystyle -13< x< 3\)

\(\displaystyle x< -13\)

Correct answer:

\(\displaystyle -13< x< 3\)

Explanation:

We want to isolate the variable on one side and numbers on another side. Treat like a normal equation. 

\(\displaystyle \left | x+5\right |< 8\) We need to set-up two equations since its absolute value.

\(\displaystyle x+5< 8\) Subtract \(\displaystyle 5\) on both sides. \(\displaystyle x< 3\)

\(\displaystyle -(x+5)< 8\) Divide \(\displaystyle -1\) on both sides which flips the sign.

\(\displaystyle x+5>-8\) Subtract \(\displaystyle 5\) on both sides. \(\displaystyle x>-13\)

Since we have the \(\displaystyle x\)'s being either greater than or less than the values, we can combine them to get \(\displaystyle -13< x< 3\).

Example Question #23 : Inequalities

Solve for \(\displaystyle x\).

\(\displaystyle \left | x+7\right |\leq3x+13\)

Possible Answers:

\(\displaystyle -3\leq x\)

\(\displaystyle 3\leq x\leq 5\)

\(\displaystyle x\leq -3, x\leq -5\)

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

\(\displaystyle -5\leq x\)

Correct answer:

\(\displaystyle -3\leq x\)

Explanation:

We want to isolate the variable on one side and numbers on another side. Treat like a normal equation. 

\(\displaystyle \left | x+7\right |\leq3x+13\) We need to set-up two equations since it's absolute value.

\(\displaystyle x+7\leq 3x+13\) Subtract \(\displaystyle x, 7\) on both sides.

\(\displaystyle -6\leq 2x\) Divide \(\displaystyle 2\) on both sides.

\(\displaystyle -3\leq x\)

\(\displaystyle -(x+7)\leq 3x+13\) Distribute the negative sign to each term in the parenthesis.

\(\displaystyle -x-7\leq3x+13\) Add \(\displaystyle x\) and subtract \(\displaystyle 13\) on both sides.

\(\displaystyle -20\leq4x\) Divide \(\displaystyle 4\) on both sides.

\(\displaystyle -5\leq x\) We must check each answer. Let's try \(\displaystyle 0\).

\(\displaystyle \left | 0+7\right |< 3(0)+13\)    \(\displaystyle 7< 13\) This is true therefore \(\displaystyle -3\leq x\) is a correct answer. Let's next try \(\displaystyle -4\).

\(\displaystyle \left | -4+7\right |< 3(-4)+13\)  \(\displaystyle 3< 1\) This is not true therefore \(\displaystyle -5\leq x\) is not correct. 

Final answer is just \(\displaystyle -3\leq x\).

Example Question #13 : New Sat Math Calculator

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:

\(\displaystyle 4\)

\(\displaystyle 8\)

\(\displaystyle 12\)

\(\displaystyle 0\)

\(\displaystyle 16\)

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.

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