PSAT Math : Equations / Inequalities

Study concepts, example questions & explanations for PSAT Math

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Example Questions

Example Question #54 : Equations / Inequalities

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.

What is the monthly break-even point at Pets Plus?

Possible Answers:

30

35

40

50

25

Correct answer:

30

Explanation:

Let x= the number of bird houses sold each month.

Revenue = 40x

Costs=15x+750

The break-even point is where the revenue is the same as the costs:

Revenue=Costs 

40x=15x+750 

Solve for x:

x=30

Therefore, Pets Plus must sell 30 bird houses to break-even.

Example Question #141 : Equations / Inequalities

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:

\$500

\$750

\$625

\$250

\$300

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 #51 : How To Find The Solution To An Equation

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 #152 : Algebra

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

Possible Answers:

10

12

14

18

16

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 #151 : Gre Quantitative Reasoning

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 #141 : Equations / Inequalities

What property of arithmetic is demonstrated here? 

Possible Answers:

Symmetric

Commutative

Reflexive

Identity

Transitive

Correct answer:

Reflexive

Explanation:

The statement expresses the idea that any number is equal to itself. This is the reflexive property of equality.

Example Question #2 : Quadratic Equation

If f(x) = -x2 + 6x - 5, then which could be the value of a if f(a) = f(1.5)?

Possible Answers:
2.5
4.5
3.5
1
4
Correct answer: 4.5
Explanation:

We need to input 1.5 into our function, then we need to input "a" into our function and set these results equal.

f(a) = f(1.5)

f(a) = -(1.5)2 +6(1.5) -5

f(a) = -2.25 + 9 - 5

f(a) = 1.75

-a2 + 6a -5 = 1.75

Multiply both sides by 4, so that we can work with only whole numbers coefficients.

-4a2 + 24a - 20 = 7

Subtract 7 from both sides.

-4a2 + 24a - 27 = 0

Multiply both sides by negative one, just to make more positive coefficients, which are usually easier to work with.

4a2 - 24a + 27 = 0

In order to factor this, we need to mutiply the outer coefficients, which gives us 4(27) = 108. We need to think of two numbers that multiply to give us 108, but add to give us -24. These two numbers are -6 and -18. Now we rewrite the equation as:

4a2 - 6a -18a + 27 = 0

We can now group the first two terms and the last two terms, and then we can factor.

(4a2 - 6a )+(-18a + 27) = 0

2a(2a-3) + -9(2a - 3) = 0

(2a-9)(2a-3) = 0

This means that 2a - 9 =0, or 2a - 3 = 0.

2a - 9 = 0

2a = 9

a = 9/2 = 4.5

2a - 3 = 0

a = 3/2 = 1.5

So a can be either 1.5 or 4.5.

The only answer choice available that could be a is 4.5.

Example Question #2 : How To Find The Solution To A Quadratic Equation

Solve for x:  2(x + 1)2 – 5 = 27

Possible Answers:

3 or –5

3 or 4

–3 or 2

–2 or 5

–2 or 4

Correct answer:

3 or –5

Explanation:

Quadratic equations generally have two answers.  We add 5 to both sides and then divide by 2 to get the quadratic expression on one side of the equation: (x + 1)2 = 16.   By taking the square root of both sides we get x + 1 = –4 or x + 1 = 4.  Then we subtract 1 from both sides to get x = –5 or x = 3.

Example Question #4 : How To Find The Solution To A Quadratic Equation

Two consecutive positive multiples of three have a product of 54. What is the sum of the two numbers?

Possible Answers:

6

15

3

9

12

Correct answer:

15

Explanation:

Define the variables to be x = first multiple of three and x + 3 = the next consecutive multiple of 3.

Knowing the product of these two numbers is 54 we get the equation x(x + 3) = 54. To solve this quadratic equation we need to multiply it out and set it to zero then factor it. So x2 + 3x – 54 = 0 becomes (x + 9)(x – 6) = 0.  Solving for x we get x = –9 or x = 6 and only the positive number is correct.  So the two numbers are 6 and 9 and their sum is 15.

Example Question #2 : Quadratic Equations

Solve 3x2 + 10x = –3

Possible Answers:

x = –1/3 or –3

x = –4/3 or –1

x = –1/6 or –6

x = –1/9 or –9

x = –2/3 or –2

Correct answer:

x = –1/3 or –3

Explanation:

Generally, quadratic equations have two answers.

First, the equations must be put in standard form: 3x2 + 10x + 3 = 0

Second, try to factor the quadratic; however, if that is not possible use the quadratic formula.

Third, check the answer by plugging the answers back into the original equation.

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