PSAT Math : Algebra

Study concepts, example questions & explanations for PSAT Math

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Example Questions

Example Question #1 : How To Solve For A Variable As Part Of A Fraction

If  , then what is the value of ?

Possible Answers:

none of these

38/3

3/38

7/12

9/114

Correct answer:

38/3

Explanation:

cross multiply:

(6)(19) = 9x

114=9x

x = 38/3

Example Question #2 : How To Solve For A Variable As Part Of A Fraction

\dpi{100} \small \frac{4 }{x} = \frac{2}{25}

Find x.

Possible Answers:

None

\dpi{100} \small 0.25

\dpi{100} \small \frac{8}{25}

\dpi{100} \small \frac{25}{8}

\dpi{100} \small 50

Correct answer:

\dpi{100} \small 50

Explanation:

Cross multiply:

\dpi{100} \small 4 \times 25 = 2x

\dpi{100} \small 100 = 2x

\dpi{100} \small x = 50

Example Question #3 : How To Solve For A Variable As Part Of A Fraction

The numerator of a fraction is the sum of 4 and 5 times the denominator. If you divide the fraction by 2, the numerator is 3 times the denominator. Find the simplified version of the fraction.

Possible Answers:

Correct answer:

Explanation:

Let numerator = N and denominator = D.

According to the first statement, 

N = (D x 5) + 4.

According to the second statement, N / 2 = 3 * D. 

Let's multiply the second equation by –2 and add itthe first equation:

–N = –6D

+[N = (D x 5) + 4]

=

–6D + (D x 5) + 4 = 0

–1D + 4 = 0

D = 4

Thus, N = 24.

Therefore, N/D = 24/4 = 6.

Example Question #671 : Algebra

Solve for :

Possible Answers:

Correct answer:

Explanation:

Solve for :

Step 1: Cross-multiply to eliminate the fraction

Step 2: Solve for :

Example Question #172 : Equations / Inequalities

Hannah is selling candles for a school fundraiser all fall. She sets a goal of selling  candles per month. The number of candles she has remaining for the month can be expressed at the end of each week by the equations , where  is the number of candles and  is the number of weeks she has sold candles this month. What is the meaning of the value  in this equation? 

Possible Answers:

The number of candles that she sells each week.

The number of candles she has remaining for the month.

The number of weeks that she has sold candles this month.

The number of candles that she has sold thus far that week.

Correct answer:

The number of candles that she sells each week.

Explanation:

Since we know that  stands for weeks, the answer has to have something to do with the weeks. This eliminates "the number of candles she has remaining for the month." Also, we can eliminate "the number of weeks that she has sold candles this month" because that would be our value for , not what we'd multiply  by. The correct answer is,  "the number of candles that she sells each week."

Example Question #1 : Translating Words To Linear Equations

We have three dogs: Joule, Newton, and Toby. Joule is three years older than twice Newton's age. Newton is Toby's age younger than eleven years. Toby is one year younger than Joules age. Find the age of each dog.

Possible Answers:

none of these

Joule: 5 years

Newton: Not born yet

Toby: 1 year

Joule: 9 years

Newton: 3 years

Toby: 8 year

Joule: 8 years

Newton: 4 years

Toby: 8 year

Joule: 12 years

Newton: 1 year

Toby: 5 year

Correct answer:

Joule: 9 years

Newton: 3 years

Toby: 8 year

Explanation:

First, translate the problem into three equations. The statement, "Joule is three years older than twice Newton's age" is mathematically translated as

where  represents Joule's age and  is Newton's age.

The statement, "Newton is Toby's age younger than eleven years" is translated as

where  is Toby's age.

The third statement, "Toby is one year younger than Joule" is

.

So these are our three equations. To figure out the age of these dogs, first I will plug the third equation into the second equation. We get

Plug this equation into the first equation to get

Solve for . Add  to both sides

Divide both sides by 3

So Joules is 9 years old. Plug this value into the third equation to find Toby's age

Toby is 8 years old. Use this value to find Newton's age using the second equation

Now, we have the age of the following dogs:

Joule: 9 years

Newton: 3 years

Toby: 8 years

Example Question #2411 : Algebra 1

Teachers at an elementary school have devised a system where a student's good behavior earns him or her tokens. Examples of such behavior include sitting quietly in a seat and completing an assignment on time. Jim sits quietly in his seat 2 times and completes assignments 3 times, earning himself 27 tokens. Jessica sits quietly in her seat 9 times and completes 6 assignments, earning herself 69 tokens. How many tokens is each of these two behaviors worth?

Possible Answers:

Sitting quietly is worth 9 tokens and completing an assignment is worth 3.

Sitting quietly is worth 7 tokens and completing an assignment is worth 3.

Sitting quietly is worth 3 tokens and completing an assignment is worth 7.

Sitting quietly is worth 3 tokens and completing an assignment is worth 9.

Sitting quietly and completing an assignment are each worth 4 tokens.

Correct answer:

Sitting quietly is worth 3 tokens and completing an assignment is worth 7.

Explanation:

Since this is a long word problem, it might be easy to confuse the two behaviors and come up with the wrong answer. Let's avoid this problem by turning each behavior into a variable. If we call "sitting quietly"  and "completing assignments" , then we can easily construct a simple system of equations, 

 

and 

.

We can multiply the first equation by  to yield .

This allows us to cancel the  terms when we add the two equations together. We get , or .

A quick substitution tells us that . So, sitting quietly is worth 3 tokens and completing an assignment on time is worth 7.

Example Question #326 : Equations / Inequalities

Solve the following story problem:

Jack and Aaron go to the sporting goods store. Jack buys a glove for  and  wiffle bats for  each. Jack has  left over. Aaron spends all his money on  hats for  each and  jerseys. Aaron started with  more than Jack. How much does one jersey cost?

Possible Answers:

Correct answer:

Explanation:

Let's call "" the cost of one jersey (this is the value we want to find)

Let's call the amount of money Jack starts with ""

Let's call the amount of money Aaron starts with ""

We know Jack buys a glove for  and  bats for  each, and then has  left over after. Thus:

simplifying,  so Jack started with 

We know Aaron buys  hats for  each and  jerseys (unknown cost "") and spends all his money.

The last important piece of information from the problem is Aaron starts with  dollars more than Jack. So:

From before we know:

Plugging in:

so Aaron started with 

Finally we plug  into our original equation for A and solve for x:

Thus one jersey costs 

Example Question #231 : Grade 8

Read, but do not solve, the following problem:

Adult tickets to the zoo sell for $11; child tickets sell for $7. One day, 6,035 tickets were sold, resulting in $50,713 being raised. How many adult and child tickets were sold? 

If  and  stand for the number of adult and child tickets, respectively, which of the following systems of equations can be used to answer this question?

Possible Answers:

Correct answer:

Explanation:

6,035 total tickets were sold, and the total number of tickets is the sum of the adult and child tickets, .

Therefore, we can say .

The amount of money raised from adult tickets is $11 per ticket mutiplied by  tickets, or  dollars; similarly,  dollars are raised from child tickets. Add these together to get the total amount of money raised:

These two equations form our system of equations.

Example Question #1 : Systems Of Inequalities

Solve the following inequality for . Round your answer to the nearest tenth.

Possible Answers:

Correct answer:

Explanation:

The first step is to square each side of the inequality.

Now simplify each side.

Now subtract the left side of the inequality to make it zero, so that we can use the quadratic formula.

Now we can use the quadratic formula.

Recall the quadratic formula.

Where , and , correspond to coefficients in the quadratic equation.

In this case  ,  , and .

Now plug these values into the quadratic equation, and we get.

Now since we are dealing with an inequality, we put the least value on the left side, and the greatest value on the right. It will look like the following.

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