ISEE Upper Level Quantitative : Equations

Study concepts, example questions & explanations for ISEE Upper Level Quantitative

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Example Questions

Example Question #681 : Isee Upper Level (Grades 9 12) Quantitative Reasoning

\(\displaystyle x(2x-9)= 35\)

Possible Answers:

\(\displaystyle x =22 \textrm{ or } x = 3 5\)

\(\displaystyle x =-5 \textrm{ or } x = 3 \frac{1}{2}\)

\(\displaystyle x =-7 \textrm{ or } x = 2 \frac{1}{2}\)

\(\displaystyle x = -2 \frac{1}{2} \textrm{ or }x =7\)

\(\displaystyle x = -3 \frac{1}{2} \textrm{ or }x =5\)

Correct answer:

\(\displaystyle x = -2 \frac{1}{2} \textrm{ or }x =7\)

Explanation:

First, rewrite the quadratic equation in standard form by distributing the \(\displaystyle x\) through the product on the left and collecting all of the terms on the left side:

\(\displaystyle x(2x-9)= 35\)

\(\displaystyle x \cdot 2x-x \cdot 9= 35\)

\(\displaystyle 2x ^{2}-9x= 35\)

\(\displaystyle 2x ^{2}-9x-35= 35 -35\)

\(\displaystyle 2x ^{2}-9x-35= 0\)

Use the \(\displaystyle ac\) method to factor the quadratic expression \(\displaystyle 2x ^{2}-9x-35\); we are looking to split the linear term by finding two integers whose sum is \(\displaystyle -9\) and whose product is \(\displaystyle 2 (-35) = -70\). These integers are \(\displaystyle -14,5\), so:

\(\displaystyle \left (2x ^{2}-14x \right ) + \left ( 5x-35 \right ) = 0\)

\(\displaystyle 2x \left (x-7 \right ) + 5\left (x-7 \right ) = 0\)

\(\displaystyle \left (2x+ 5 \right ) \left (x-7 \right ) = 0\)

Set each expression equal to 0 and solve:

\(\displaystyle 2x+5 = 0\)

\(\displaystyle 2x=-5\)

\(\displaystyle x = - \frac{5}{2} = -2 \frac{1}{2}\)

or 

\(\displaystyle x-7 = 0\)

\(\displaystyle x=7\)

The solution set is \(\displaystyle \left \{ -2 \frac{1}{2}, 7\right \}\).

Example Question #12 : Equations

Consider the line of the equation \(\displaystyle 0.9x + 0.7y = 100\)

Which is the greater quantity?

(a) The \(\displaystyle x\)-coordinate of the \(\displaystyle x\)-intercept

(b) The \(\displaystyle y\)-coordinate of the \(\displaystyle y\)-intercept

Possible Answers:

(a) and (b) are equal

It is impossible to tell from the information given

(b) is greater

(a) is greater

Correct answer:

(b) is greater

Explanation:

(a) To find the \(\displaystyle x\)-coordinate of the \(\displaystyle x\)-intercept, substitute \(\displaystyle y = 0\):

\(\displaystyle 0.9x + 0.7y = 100\)

\(\displaystyle 0.9x + 0.7 \cdot 0 = 100\)

\(\displaystyle 0.9x + 0 = 100\)

\(\displaystyle 0.9x = 100\)

\(\displaystyle 0.9x \div 0.9 = 100 \div 0.9\)

\(\displaystyle x = 100 \div 0.9 = 1,000 \div 9 = 111 \frac {1}{9}\)

(b) To find the \(\displaystyle y\)-coordinate of the \(\displaystyle y\)-intercept, substitute \(\displaystyle x = 0\):

\(\displaystyle 0.9x + 0.7y = 100\)

\(\displaystyle 0.9 \cdot 0 + 0.7y = 100\)

\(\displaystyle 0 + 0.7y = 100\)

\(\displaystyle 0.7y = 100\)

\(\displaystyle 0.7y \div 0.7 = 100 \div 0.7\) 

\(\displaystyle y =100 \div 0.7 = 1,000 \div 7 = 142\frac {6} {7}\)

(b) is the greater quantity.

Example Question #11 : How To Find The Solution To An Equation

\(\displaystyle | 50 - t | = 30\)

Which is the greater quantity?

(a) \(\displaystyle t\)

(b) 0 

Possible Answers:

(b) is greater

(a) and (b) are equal

(a) is greater

It is impossible to tell from the information given

Correct answer:

(a) is greater

Explanation:

\(\displaystyle | 50 - t | = 30\) can be rewritten as a compound statement:

\(\displaystyle 50 - t = 30\) or \(\displaystyle 50 - t = -30\)

Solve both:

\(\displaystyle 50 - t = 30\)

\(\displaystyle 50 - t - 50 = 30 - 50\)

\(\displaystyle -t = -20\)

\(\displaystyle t = 20\)

or 

\(\displaystyle 50 - t = -30\)

\(\displaystyle 50 - t -50 = -30-50\)

\(\displaystyle -t = -80\)

\(\displaystyle t = 80\)

Either way, \(\displaystyle t > 0\), so (a) is the greater quantity

Example Question #12 : Equations

Consider the line of the equation \(\displaystyle \frac{1}{99}x + \frac{1}{101}y = 1\)

Which is the greater quantity?

(a) The \(\displaystyle x\)-coordinate of the \(\displaystyle x\)-intercept

(b) The \(\displaystyle y\)-coordinate of the \(\displaystyle y\)-intercept

Possible Answers:

(a) and (b) are equal

(a) is greater

(b) is greater

It is impossible to tell from the information given

Correct answer:

(b) is greater

Explanation:

(a) To find the \(\displaystyle x\)-coordinate of the \(\displaystyle x\)-intercept, substitute \(\displaystyle y = 0\):

\(\displaystyle \frac{1}{99}x + \frac{1}{101}y = 1\)

\(\displaystyle \frac{1}{99}x + \frac{1}{101} \cdot 0 = 1\)

\(\displaystyle \frac{1}{99}x + 0 = 1\)

\(\displaystyle \frac{1}{99}x = 1\)

\(\displaystyle \frac{1}{99}x \cdot 99= 1\cdot 99\)

\(\displaystyle x= 99\)

(b) To find the \(\displaystyle y\)-coordinate of the \(\displaystyle y\)-intercept, substitute \(\displaystyle x = 0\):

\(\displaystyle \frac{1}{99}x + \frac{1}{101}y = 1\)

\(\displaystyle \frac{1}{99} \cdot 0 + \frac{1}{101}y = 1\)

\(\displaystyle 0 + \frac{1}{101}y = 1\)

\(\displaystyle \frac{1}{101}y = 1\)

\(\displaystyle \frac{1}{101}y \cdot 101 = 1\cdot 101\)

\(\displaystyle y = 101\)

This makes (b) the greater quantity

 

Example Question #12 : How To Find The Solution To An Equation

\(\displaystyle \left \lfloor N\right \rfloor\) refers to the greatest integer less than or equal to \(\displaystyle N\).

\(\displaystyle x\) and \(\displaystyle y\) are integers. Which is greater?

(a) \(\displaystyle \left \lfloor x+ y\right \rfloor\)

(b) \(\displaystyle \left \lfloor x\right \rfloor + \left \lfloor y\right \rfloor\)

Possible Answers:

It is impossible to tell from the information given

(a) and (b) are equal

(b) is greater

(a) is greater

Correct answer:

(a) and (b) are equal

Explanation:

If \(\displaystyle N\) is an integer, then \(\displaystyle \left \lfloor N\right \rfloor = N\) by definition.

Since \(\displaystyle x, y\), and, by closure, \(\displaystyle x + y\) are all integers, 

\(\displaystyle \left \lfloor x+ y\right \rfloor = x + y\) and \(\displaystyle \left \lfloor x\right \rfloor + \left \lfloor y\right \rfloor = x + y\), making (a) and (b) equal.

Example Question #15 : Algebraic Concepts

Consider the line of the equation \(\displaystyle 5x + 4y = -200\).

Which is the greater quantity?

(a) The \(\displaystyle x\)-coordinate of the \(\displaystyle x\)-intercept.

(b) The \(\displaystyle y\)-coordinate of the \(\displaystyle y\)-intercept.

Possible Answers:

(b) is greater.

(a) and (b) are equal.

It is impossible to tell from the information given.

(a) is greater.

Correct answer:

(a) is greater.

Explanation:

(a) To find the \(\displaystyle x\)-coordinate of the \(\displaystyle x\)-intercept, substitute \(\displaystyle y = 0\):

\(\displaystyle 5x + 4y = -200\)

\(\displaystyle 5x + 4 \cdot 0 = -200\)

\(\displaystyle 5x + 0 = -200\)

\(\displaystyle 5x = -200\)

\(\displaystyle 5x\div 5= -200\div 5\)

\(\displaystyle x = -40\)

(b) To find the \(\displaystyle y\)-coordinate of the \(\displaystyle y\)-intercept, substitute \(\displaystyle x = 0\):

\(\displaystyle 5x + 4y = -200\)

\(\displaystyle 5 \cdot 0 + 4y = -200\)

\(\displaystyle 0 + 4y = -200\)

\(\displaystyle 4y = -200\)

\(\displaystyle 4y \div 4= -200 \div 4\)

\(\displaystyle y = -50\)

Therefore (a) is the greater quantity.

Example Question #691 : Isee Upper Level (Grades 9 12) Quantitative Reasoning

\(\displaystyle | 45 - t | = 60\)

\(\displaystyle | 45 - u | = 50\)

Which is the greater quantity?

(a) \(\displaystyle t\)

(b) \(\displaystyle u\)

Possible Answers:

It is impossible to tell from the information given.

(b) is greater.

(a) is greater.

(a) and (b) are equal.

Correct answer:

It is impossible to tell from the information given.

Explanation:

Each can be rewritten as a compound statement. Solve separately:

\(\displaystyle | 45 - t | = 60\)

\(\displaystyle 45 - t =- 60 \textrm{ or }45 - t = 60\)

\(\displaystyle 45 - t =- 60\)

\(\displaystyle 45 - t -45 =- 60 -45\)

\(\displaystyle -t = -105\)

\(\displaystyle t = 105\)

or 

\(\displaystyle 45 - t = 60\)

\(\displaystyle 45 - t -45 =60 -45\)

\(\displaystyle -t = 15\)

\(\displaystyle t = -15\)

 

Similarly:

\(\displaystyle | 45 - u | = 50\)

\(\displaystyle 45 - u = -50 \textrm{ or } 45 - u = 50\)

\(\displaystyle 45 - u = -50\)

\(\displaystyle 45 - u -45 = -50 -45\)

\(\displaystyle - u = -95\)

\(\displaystyle u =95\)

 

\(\displaystyle 45 - u = 50\)

\(\displaystyle 45 - u -45 = 50 -45\)

\(\displaystyle - u = 5\)

\(\displaystyle u = -5\)

 

Therefore, it cannot be determined with certainty which of \(\displaystyle t\) and \(\displaystyle u\) is the greater.

Example Question #13 : How To Find The Solution To An Equation

\(\displaystyle | t - 10 | = 40\)

Which is the greater quantity?

(a) \(\displaystyle t\)

(b) \(\displaystyle 50\)

Possible Answers:

(a) is greater.

It is impossible to tell from the information given.

(b) is greater.

(a) and (b) are equal.

Correct answer:

It is impossible to tell from the information given.

Explanation:

If \(\displaystyle | t - 10 | = 40\), then either \(\displaystyle t - 10 = 40\) or  \(\displaystyle t - 10 = -40\). Solve for \(\displaystyle t\) in both equations:

\(\displaystyle t - 10 = 40\)

\(\displaystyle t - 10 + 10 = 40 + 10\)

\(\displaystyle t = 50\)

or 

\(\displaystyle t - 10 = -40\)

\(\displaystyle t - 10 + 10 = -40 + 10\)

\(\displaystyle t = -30\)

Therefore, either (a) and (b) are equal or (b) is the greater quantity, but it cannot be determined with certainty.

Example Question #12 : How To Find The Solution To An Equation

\(\displaystyle t^3 = -125\)

Which is the greater quantity?

(a) \(\displaystyle t\)

(b) \(\displaystyle -5\)

Possible Answers:

(b) is greater

(a) and (b) are equal

(a) is greater

It is impossible to tell from the information given

Correct answer:

(a) and (b) are equal

Explanation:

\(\displaystyle t^3 = -125\)

\(\displaystyle \sqrt[3]{t^3 }=\sqrt[3]{ -125}\)

\(\displaystyle \sqrt[3]{t^3 }= -\sqrt[3]{ 125}\)

\(\displaystyle t= -5\)

Example Question #12 : Algebraic Concepts

Consider the line of the equation \(\displaystyle 4x + 5y = 100\).

Which is the greater quantity?

(a) The \(\displaystyle x\)-coordinate of the \(\displaystyle x\)-intercept

(b) The \(\displaystyle y\)-coordinate of the \(\displaystyle y\)-intercept

Possible Answers:

(a) and (b) are equal.

(a) is greater.

It is impossible to tell from the information given.

(b) is greater.

Correct answer:

(a) is greater.

Explanation:

(a) To find the \(\displaystyle x\)-coordinate of the \(\displaystyle x\)-intercept, substitute \(\displaystyle y = 0\):

\(\displaystyle 4x + 5y = 100\)

\(\displaystyle 4x + 5 \cdot 0 = 100\)

\(\displaystyle 4x + 0 = 100\)

\(\displaystyle 4x = 100\)

\(\displaystyle 4x \div 4 = 100 \div 4\)

\(\displaystyle x = 25\)

(b) To find the \(\displaystyle y\)-coordinate of the \(\displaystyle y\)-intercept, substitute \(\displaystyle x = 0\):

\(\displaystyle 4x + 5y = 100\)

\(\displaystyle 4\cdot 0 + 5y = 100\)

\(\displaystyle 5y = 100\)

\(\displaystyle 5y \div 5 = 100\div 5\)

\(\displaystyle y = 20\)

(a) is the greater quantity.

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