GRE Math : How to find the solution to an equation

Study concepts, example questions & explanations for GRE Math

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Example Questions

Example Question #91 : How To Find The Solution To An Equation

Pets Plus makes bird houses.  Their monthly fixed expenses are $750.  The cost for each bird house is $15.  The bird houses sell for $40.

If Pets Plus sells 50 bird houses, what is the profit?

Possible Answers:

\$625

\$300

\$500

\$750

\$250

Correct answer:

\$500

Explanation:

Let x = the number of birdhouses sold each month.

Revenue=40x

Costs=15x+750

Profit = Revenue-Costs 

=40x-15x-750 

=25x-750

Substituting in 50 for x gives an answer of 500, so the profit on 50 birdhouses is $500.

Example Question #52 : Algebra

George is three times older than Joey.  The sum of their ages is 16.  What is the product of their ages?

Possible Answers:

Correct answer:

Explanation:

Let  = Joey's age and  = George's age.

Then the equation to solve becomes .

Therefore, Joey is 4 years old and George is 12 years old, so the product of their ages is 48.

Example Question #53 : Algebra

Three consecutive even numbers add to 42.  What is the middle number?

Possible Answers:

18

16

14

10

12

Correct answer:

14

Explanation:

Let x = 1st even number, x+2 = 2nd even number, and x+4 = 3rd even number.

Then the equation to solve becomes x+(x+2)+(x+4)=42.

3x+6=42

Thus x=12,x+2=14,\ and\ x+4=16, so the middle number is 14.

Example Question #51 : Equations / Inequalities

Consider the following equation:

Which of the following must be true?

Possible Answers:

Correct answer:

Explanation:

The quantity inside the absolute value brackets must equal either  or , depending on whether the quantity inside the brackets is positive or negative. We therefore have two seperate equations:

To solve the first equation, add 9 to both sides:

Subtract  from both sides:

This is the first solution. Now let's look at the second equation. The distributive law gives us:

Add 9 to both sides:

Add  to both sides:

Divide both sides by 3:

Therefore, is either 4 or 6. 

Statement  does NOT have to be true because  can also equal 4.

Statement  must be true because both 4 and 6 are positive .

Finally, statement  always holds because 4 and 6 are both even. 

Example Question #51 : Algebra

If

,

then 

Possible Answers:

Correct answer:

Explanation:

Divide both sides by 300 to get .  Subtract 7 and divide by two to get .

Example Question #151 : Gre Quantitative Reasoning

If b – 3 = a, then (a – b)2 =

Possible Answers:

–9

–3

3

The answer cannot be determined from the given information.

9

Correct answer:

9

Explanation:

The quantity can be regrouped to be –3 = a – b.  Thus, (a – b)2 = (–3)2 = 9.

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