SAT Math : Linear / Rational / Variable Equations

Study concepts, example questions & explanations for SAT Math

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Example Questions

Example Question #1862 : Sat Mathematics

\(\displaystyle | 3y - 17| + 12 = 49\).

Which of the following is a solution of this equation?

Possible Answers:

\(\displaystyle y = -14\frac{2}{3}\) 

\(\displaystyle y = -18\)

\(\displaystyle y = 26\)

\(\displaystyle y = -6 \frac{2}{3}\)

\(\displaystyle y = 14\frac{2}{3}\)

Correct answer:

\(\displaystyle y = -6 \frac{2}{3}\)

Explanation:

To solve for the variable we must move all constants to the other side of the equation. Since we have absolute value bars in the particular equation we will first move all constants that are outside of the absolute value bars. To do this apply the oppisite operation. In this particular case, subtract twelve from both sides.

\(\displaystyle | 3y - 17| + 12 = 49\)

\(\displaystyle | 3y - 17| + 12 - 12 = 49 - 12\)

\(\displaystyle | 3y - 17| = 37\)

Now we will deal with the absolute value bars which state that the quantity inside them can be positive of negative.

Either

\(\displaystyle 3y - 17= -37\) or \(\displaystyle 3y - 17= 37\).

Solve each separately:

\(\displaystyle 3y - 17= -37\)

\(\displaystyle 3y - 17+ 17 = -37 + 17\)

\(\displaystyle 3y = -20\)

\(\displaystyle \frac{3y}{3} = \frac{-20}{3}\)

\(\displaystyle y = -6 \frac{2}{3}\)

 

\(\displaystyle 3y - 17= 37\)

\(\displaystyle 3y - 17+17 = 37+17\)

\(\displaystyle 3y = 54\)

\(\displaystyle \frac{3y}{3} = \frac{54}{3}\)

\(\displaystyle y = 18\)

 Therefore, \(\displaystyle y = -6 \frac{2}{3}\) or \(\displaystyle y = 18\).

The correct choice is  \(\displaystyle y = -6 \frac{2}{3}\).

Example Question #1863 : Sat Mathematics

\(\displaystyle 125 - |4t-98| = 113\)

Give the solution set to this equation.

Possible Answers:

\(\displaystyle t= 21\frac{1}{2}\)  or \(\displaystyle t= -27\frac{1}{2}\)

The equation has no solution.

\(\displaystyle t= -21\frac{1}{2}\) or \(\displaystyle t= 27\frac{1}{2}\)

\(\displaystyle t= 21\frac{1}{2}\) or \(\displaystyle t= 27\frac{1}{2}\)

\(\displaystyle t= -21\frac{1}{2}\) or \(\displaystyle t= -27\frac{1}{2}\)

Correct answer:

\(\displaystyle t= 21\frac{1}{2}\) or \(\displaystyle t= 27\frac{1}{2}\)

Explanation:

To solve for the variable we must move all constants to the other side of the equation. Since we have absolute value bars in the particular equation we will first move all constants that are outside of the absolute value bars. To do this apply the oppisite operation. In this particular case, subtract 125 from both sides.

\(\displaystyle 125 - |4t-98| = 113\)

\(\displaystyle 125 - |4t-98| - 125 = 113 - 125\)

\(\displaystyle - |4t-98| =-12\)

\(\displaystyle |4t-98| =12\)

\(\displaystyle 4t-98 = -12\) or \(\displaystyle 4t-98 = 12\)

Solve separately:

\(\displaystyle 4t-98 = -12\)

\(\displaystyle 4t-98 + 98 = -12 + 98\)

\(\displaystyle 4t = 86\)

\(\displaystyle \frac{4t}{4} = \frac{86 }{4}\)

\(\displaystyle t= 21\frac{1}{2}\)

 

\(\displaystyle 4t-98 = 12\)

\(\displaystyle 4t-98 + 98 = 12 + 98\)

\(\displaystyle 4t = 110\)

\(\displaystyle \frac{4t}{4} = \frac{110 }{4}\)

\(\displaystyle t= 27\frac{1}{2}\)

 

 

Example Question #91 : Equations / Inequalities

James is an artist and makes \(\displaystyle p\) number of portraits per month.  At this rate, how many months will it take him to paint \(\displaystyle t\) portraits?

Possible Answers:

\(\displaystyle 10t\)

\(\displaystyle \frac{100p}{t}\)

\(\displaystyle \frac{p}{t}\)

\(\displaystyle \frac{t}{p}\)

\(\displaystyle pt\)

Correct answer:

\(\displaystyle \frac{t}{p}\)

Explanation:

To figure out the total portraits done by James, you must multiply rate \(\displaystyle p\) by the number of months \(\displaystyle m\).  This equation would be \(\displaystyle pm=t\).  To solve for the number of months \(\displaystyle m\) you must divide both sides by \(\displaystyle p\). This gives us \(\displaystyle m=\frac{t}{p}\).

Example Question #1865 : Sat Mathematics

Point \(\displaystyle A\) lies on the line with the equation \(\displaystyle y-2=8(x-3)\).  If the \(\displaystyle x\)-coordinate for \(\displaystyle A\) is \(\displaystyle 5\), what is the \(\displaystyle y\)-coordinate?

Possible Answers:

\(\displaystyle 16\)

\(\displaystyle 20\)

\(\displaystyle 36\)

\(\displaystyle 9\)

\(\displaystyle 18\)

Correct answer:

\(\displaystyle 18\)

Explanation:

The first step is to simplify your equation.  You distribute \(\displaystyle 8\) to get \(\displaystyle y-2=8x-24\).  Then to get \(\displaystyle y\) by itself you add \(\displaystyle 2\) to both sides ending with \(\displaystyle y=8x-22\).  Finally insert the \(\displaystyle x\)-coordinate to get \(\displaystyle 8(5)-22\) which equals \(\displaystyle 18\).

Example Question #92 : Equations / Inequalities

If \(\displaystyle 3(a-6)=81\), then \(\displaystyle a\) is equal to what?

Possible Answers:

\(\displaystyle 33\)

\(\displaystyle 90\)

\(\displaystyle 21\)

\(\displaystyle 63\)

\(\displaystyle 27\)

Correct answer:

\(\displaystyle 33\)

Explanation:

To get \(\displaystyle a\) by itself, divide each side by \(\displaystyle 3\) to get \(\displaystyle a-6=27\).  Then add \(\displaystyle 6\) to both sides to get \(\displaystyle a=33\).

Example Question #92 : Linear / Rational / Variable Equations

Which of the following equations has as its solution set \(\displaystyle \left \{ -18.5, 10.5 \right \}\) ?

Possible Answers:

\(\displaystyle |2x + 7| = 28\)

\(\displaystyle |2x + 8 | = 29\)

\(\displaystyle |2x + 6| = 27\)

\(\displaystyle |2x + 9| = 30\)

\(\displaystyle |2x + 10| = 31\)

Correct answer:

\(\displaystyle |2x + 8 | = 29\)

Explanation:

The absolute value of a nonnegative number is the number itself; the absolute value of a negative number is its positive opposite.

By substitution, 10.5 can be seen to be a solution of each of the equations in the five choices. For example:

\(\displaystyle |2x + 6| = 27\)

\(\displaystyle |2 \cdot 10.5 + 6| = 27\)

\(\displaystyle |21 + 6| = 27\)

\(\displaystyle |27 | = 27\) - a true statement.

That 10.5 is a solution of the other four equations can be proved similarly. Therefore, the question is essentially to choose the equation with \(\displaystyle -18.5\) as its other solution. Again, we can do this using substitution in each equations. We see that \(\displaystyle |2x + 8 | = 29\) is correct as follows:

\(\displaystyle |2x + 8 | = 29\)

\(\displaystyle |2 (-18.5) + 8 | = 29\)

\(\displaystyle |-37 + 8 | = 29\)

\(\displaystyle |-29| = 29\) - a true statement.

Similar substitution in the other four statements shows that \(\displaystyle -18.5\) is not a solution of any of them; for example, in \(\displaystyle |2x + 9| = 30\):

\(\displaystyle |2x + 9| = 30\)

\(\displaystyle |2 (-18.5) + 9| = 30\)

\(\displaystyle |-37+ 9| = 30\)

\(\displaystyle |-28| = 30\)

\(\displaystyle 28 = 30\) - a false statement.

 

Example Question #91 : Algebra

High and low 2

Above is a graph which gives the high and low temperatures, in degrees Celsius, over a one week period for Washington City. Temperature given in degrees Celsius can be converted to the Fahrenheit scale using the following formula, where \(\displaystyle C\) and \(\displaystyle F\) are the temperature expressed in degrees Celsius and degrees Fahrenheit, respectively:

\(\displaystyle F =1.8 C + 32\)

On how many days of the week shown on the graph did the temperature get above \(\displaystyle 75 ^{\circ } F\)?

Possible Answers:

Four

Five

Six

Three

Seven

Correct answer:

Three

Explanation:

Convert \(\displaystyle 75 ^{\circ } F\) to the Celsius scale by setting \(\displaystyle F = 75\) in the conversion formula and solving for \(\displaystyle C\):

\(\displaystyle 1.8 C + 32 = F\)

\(\displaystyle 1.8 C + 32 = 75\)

\(\displaystyle 1.8 C + 32 - 32 = 75 - 32\)

\(\displaystyle 1.8 C = 43\)

\(\displaystyle 1.8 C \div 1.8 = 43 \div 1.8\)

\(\displaystyle C \approx 23.9\)

The question is therefore asking for the number of days that the temperature topped \(\displaystyle 23.9^{\circ } C\). Examine the graph below:

High and low 3

The high temperature was greater than \(\displaystyle 23.9^{\circ } C\) on Tuesday, Friday, and Saturday - three different days.

Example Question #51 : How To Find The Solution To An Equation

Tommy's and Sara's current ages are represented by t and s, respectively. If in five years, Tommy will be twice as old as Sara, which of the following represents t in terms of s?

Possible Answers:

\(\displaystyle t = 2s + 10\)

\(\displaystyle t = 2s -5\)

\(\displaystyle t = s + 5\)

\(\displaystyle t = s + 10\)

\(\displaystyle t = 2s + 5\)

Correct answer:

\(\displaystyle t = 2s + 5\)

Explanation:

Tommy's current age is represented by t, and Sara's is represented by s. In five years, both Tommy's and Sara's ages will be increased by five. Thus, in five years, we can represent Tommy's age as \(\displaystyle t + 5\)and Sara's as \(\displaystyle s + 5\).

The problem tells us that Tommy's age in five years will be twice as great as Sara's in five years. Thus, we can write an algebraic expression to represent the problem as follows:

\(\displaystyle t + 5 = 2(s + 5)\)

In order to solve for t, first simplify the right side by distributing the 2.

\(\displaystyle t + 5 = 2s + 10\)

Then subtract 5 from both sides.

\(\displaystyle t = 2s + 5\)

The answer is \(\displaystyle t = 2s + 5\).

Example Question #92 : Algebra

If Billy runs at a pace of \(\displaystyle 10\: \frac{\text{m}}{\text{sec}}\), how long will it take billy to run \(\displaystyle 549\:\text{m}\)?

Possible Answers:

\(\displaystyle 54\:\text{sec}\)

\(\displaystyle 59\:\text{sec}\)

\(\displaystyle 55\:\text{sec}\)

\(\displaystyle 50\:\text{sec}\)

\(\displaystyle 54.9\:\text{sec}\)

Correct answer:

\(\displaystyle 54.9\:\text{sec}\)

Explanation:

In order to solve this, we need to set up an equation. \(\displaystyle 549\:\text{m}=\frac{10\:\text{m}}{\text{sec}}\cdot x\), where \(\displaystyle x\) is time. All we need to do is divide by \(\displaystyle 10\: \frac{\text{m}}{\text{sec}}\) on each side.

\(\displaystyle 549\:\text{m}=\frac{10\:\text{m}}{\text{s}}\cdot x\)

\(\displaystyle \frac{549\:\text{m}}{\frac{10\:\text{m}}{\text{sec}}}=x\)

\(\displaystyle \frac{549\:\text{m\:sec}}{10\:\text{m}}=x\)

\(\displaystyle x=\frac{549\:\text{sec}}{10}=54.9\:\text{sec}\)

Example Question #91 : Linear / Rational / Variable Equations

Rocket \(\displaystyle A\) is launched from the ground at \(\displaystyle 25\:\frac{\text{m}}{\text{s}}\), and Rocket \(\displaystyle B\) is launched \(\displaystyle 3\:\text{m}\) off the ground at \(\displaystyle 16\:\frac{m}{s}\). At what time will Rocket \(\displaystyle A\) and Rocket \(\displaystyle B\) cross path's?

Possible Answers:

\(\displaystyle \frac{1}{3}\)

\(\displaystyle 1\)

\(\displaystyle \frac{2}{3}\)

\(\displaystyle 3\)

\(\displaystyle 2\)

Correct answer:

\(\displaystyle \frac{1}{3}\)

Explanation:

First we need to create equations that represent the path's of the Rocket's.

For Rocket \(\displaystyle A\), the equation is

\(\displaystyle y=25x\)

For Rocket \(\displaystyle B\), the equation is

\(\displaystyle y=16x+3\)

In order to solve for the time the Rocket's cross, we need to set the equations equal to each other.

\(\displaystyle 25x=16x+3\)

Now solve for \(\displaystyle x\)

\(\displaystyle 9x=3\)

\(\displaystyle x=\frac{1}{3}\)

 

 

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