ISEE Middle Level Quantitative : How to multiply variables

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

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Example Questions

Example Question #31 : Operations

Mulitply:

\(\displaystyle (x-7 )(x+5)\)

Possible Answers:

\(\displaystyle x^{2} +2x-35\)

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

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

\(\displaystyle x^{2} -35x-12\)

\(\displaystyle x^{2} -12x-35\)

Correct answer:

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

Explanation:

The FOIL method works nicely here:

\(\displaystyle (x-7 )(x+5) = x \cdot x + x \cdot5 + (-7) \cdot x + (-7) \cdot 5 = x^{2} +5x -7x -35 = x^{2} - 2x -35\)

Example Question #2 : How To Multiply Variables

Which quantity is greater?

\(\displaystyle (a)\ (2)^{-3}\)

\(\displaystyle (b)\ (-2)^{3}\)

Possible Answers:

\(\displaystyle (a)\)  is greater

It is not possible to tell from the information given

\(\displaystyle (a)\) and \(\displaystyle (b)\) are equal

\(\displaystyle (b)\)  is greater

Correct answer:

\(\displaystyle (a)\)  is greater

Explanation:

\(\displaystyle (a) =(2)^{-3} = \frac{1}{(2)^{3}}=\frac{1}{8}\)

\(\displaystyle (b)= (-2)^{3}=(-2)(-2)(-2)=-8\)

\(\displaystyle (a)\)  is the greater amount.

Example Question #31 : Isee Middle Level (Grades 7 8) Quantitative Reasoning

Which quantity is greater?

\(\displaystyle (a)\ (-\frac{1}{2})^{4}\)

\(\displaystyle (b)\ (-\frac{1}{2})^{-4}\)

Possible Answers:

\(\displaystyle (a)\) and \(\displaystyle (b)\) are equal

\(\displaystyle (b)\) is greater

\(\displaystyle (a)\) is greater

It is not possible to tell from the information given

Correct answer:

\(\displaystyle (b)\) is greater

Explanation:

 \(\displaystyle (a)= (-\frac{1}{2})^{4} = (-\frac{1}{2})(-\frac{1}{2})(-\frac{1}{2})(-\frac{1}{2})=\frac{1}{16}\)

\(\displaystyle (b) =(-\frac{1}{2})^{-4}=\frac{1}{(-\frac{1}{2})^{4}}=\frac{1}{(-\frac{1}{2})(-\frac{1}{2})(-\frac{1}{2})(-\frac{1}{2})}=\frac{1}{\frac{1}{16}}=16\)

\(\displaystyle (b)\) is the greater amount.

Example Question #34 : Isee Middle Level (Grades 7 8) Quantitative Reasoning

Which quantity is greater?

\(\displaystyle (a)\ (3)^{-2}\)

\(\displaystyle (b)\ (\frac{1}{3})^{2}\)

Possible Answers:

\(\displaystyle (b)\) is greater

It is not possible to tell from the information given

\(\displaystyle (a)\) and \(\displaystyle (b)\) are equal

\(\displaystyle (a)\) is greater

Correct answer:

\(\displaystyle (a)\) and \(\displaystyle (b)\) are equal

Explanation:

\(\displaystyle (a)= (3)^{-2}=\frac{1}{3^{2}}=\frac{1}{9}\)

\(\displaystyle (b)=(\frac{1}{3})^{2}=(\frac{1}{3})(\frac{1}{3})=\frac{1}{9}\)

 \(\displaystyle (a)\) and \(\displaystyle (b)\) are equal.

Example Question #35 : Isee Middle Level (Grades 7 8) Quantitative Reasoning

Which quantity is greater?

\(\displaystyle (a)\ -4(x^{2}+2x-10)\)

\(\displaystyle (b)\ -4x^2-8x-40\)

Possible Answers:

\(\displaystyle (a)\) is greater

It is not possible to tell from the information given

\(\displaystyle (b)\) is greater

\(\displaystyle (a)\) and \(\displaystyle (b)\) are equal

Correct answer:

\(\displaystyle (a)\) is greater

Explanation:

\(\displaystyle (a)= -4(x^{2}+2x-10)\)

Use the distributive property to expand.

\(\displaystyle (a)= (-4)x^2+(-4)(2x)-(-4)(10)\)

 

\(\displaystyle (a)=-4x^2-8x+40\)

\(\displaystyle (b) =-4x^2-8x-40\)

To compare the expressions, we can remove common factors. \(\displaystyle (-4x^2)\) and \(\displaystyle (-8x)\) are common in both expressions, so they can be removed:

\(\displaystyle (a)=(-4x^2-8x)+40\)

\(\displaystyle (b)=(-4x^2-8x)-40\)

\(\displaystyle 40>-40\)

\(\displaystyle -4x^2-8x+40>-4x^2-8x-40\)

\(\displaystyle (a)>(b)\)

Example Question #36 : Isee Middle Level (Grades 7 8) Quantitative Reasoning

Which quantity is greater?

\(\displaystyle (a)\ -3(x^3+1)\)

\(\displaystyle (b)\ 3(-x^3+1)\)

Possible Answers:

\(\displaystyle (a)\) is greater

\(\displaystyle (b)\) is greater

It is not possible to tell from the information given

\(\displaystyle (a)\) and \(\displaystyle (b)\) are equal

Correct answer:

\(\displaystyle (b)\) is greater

Explanation:

Use the distributive property to evaluate \(\displaystyle (a)\) and \(\displaystyle (b)\).

\(\displaystyle (a)= -3(x^3+1)=-3x^3-3\)

\(\displaystyle (b)= 3(-x^3+1)=-3x^3+3\)

Since \(\displaystyle 3>-3\), we get:

\(\displaystyle -3x^3+3>-3x^3-3\)

\(\displaystyle (b)>(a)\)

\(\displaystyle (b)\) is the greater quantity.

Example Question #37 : Isee Middle Level (Grades 7 8) Quantitative Reasoning

Which quantity is greater?

\(\displaystyle (a)\ -2(x^4+x^2-7)\)

\(\displaystyle (b)\ 2(-x^4-x^2+6)\)

Possible Answers:

\(\displaystyle (a)\) is greater

\(\displaystyle (a)\) and \(\displaystyle (b)\) are equal

\(\displaystyle (b)\) is greater

It is not possible to tell from the information given

Correct answer:

\(\displaystyle (a)\) is greater

Explanation:

Use the distributive property to evaluate each quantity.

\(\displaystyle (a) =-2(x^{4}+x^2-7)\)

\(\displaystyle (a)= (-2)x^4+(-2)(x^2)-(-2)(7)\)

\(\displaystyle (a)=-2x^4-2x^2+14\)

 

\(\displaystyle (b)= 2(-x^4-x^2+6)\)

\(\displaystyle (b)= -(2)x^4-(2)(x^2)+(2)(6)\)

\(\displaystyle (b)= -2x^4-2x^2+12\)

 

\(\displaystyle (-2x^4)\) and \(\displaystyle (-2x^2)\) are common in both expressions, so we can write:

\(\displaystyle 14>12\)

\(\displaystyle -2x^4-2x^2+14>-2x^4-2x^2+12\)

\(\displaystyle (a)>(b)\)

\(\displaystyle (a)\) is the greater quantity

Example Question #2 : How To Multiply Variables

Which quantity is greater?

\(\displaystyle (a)\ (9)^{-2}\)

\(\displaystyle (b)\ (-3)^{-4}\)

Possible Answers:

\(\displaystyle (a)\) is greater

It is not possible to tell from the information given

\(\displaystyle (b)\) is greater

\(\displaystyle (a)\) and \(\displaystyle (b)\) are equal

Correct answer:

\(\displaystyle (a)\) and \(\displaystyle (b)\) are equal

Explanation:

\(\displaystyle (a)\ (9)^{-2}=\frac{1}{9^2}=\frac{1}{81}\)

\(\displaystyle (b)\ (-3)^{-4}=\frac{1}{(-3)^4}=\frac{1}{(-3)(-3)(-3)(-3)}=\frac{1}{81}\)

 \(\displaystyle (a)\) and \(\displaystyle (b)\) are equal.

Example Question #39 : Isee Middle Level (Grades 7 8) Quantitative Reasoning

Which quantity is greater?

\(\displaystyle (a)\ (-4)^{-2}\)

\(\displaystyle (b)\ (-4)^{2}\)

Possible Answers:

It is not possible to tell from the information given

\(\displaystyle (a)\) is greater

\(\displaystyle (a)\) and \(\displaystyle (b)\) are equal

\(\displaystyle (b)\) is greater

Correct answer:

\(\displaystyle (b)\) is greater

Explanation:

 \(\displaystyle (a) =(-4)^{-2} = \frac{1}{(-4)^{2}}=\frac{1}{(-4)(-4)}=\frac{1}{16}\)

\(\displaystyle (b)= (-4)^{2}=(-4)(-4)=16\)

\(\displaystyle (b)\) is the greater amount.

Example Question #40 : Isee Middle Level (Grades 7 8) Quantitative Reasoning

Which of the following is equivalent to \(\displaystyle 20y\) ?

Possible Answers:

All four of the expressions given in the other responses are correct.

\(\displaystyle 5(3y + y)\)

\(\displaystyle 4 (5y)\)

\(\displaystyle 5 (4y)\)

\(\displaystyle 4 (3y + 2y)\)

Correct answer:

All four of the expressions given in the other responses are correct.

Explanation:

We demonstrate that all four of the expressions are equivalent to \(\displaystyle 20y\).

By the associative property of multiplication,

\(\displaystyle 4 (5y) = (4 \cdot 5) \cdot y = 20y\)

and

\(\displaystyle 5 (4y) = (5\cdot 4) \cdot y = 20y\)

By combining like terms, and applying the distribution property:

\(\displaystyle 5(3y + y) = 5(3y + 1 y) = 5[ (3 + 1 ) y] = 5 \left ( 4 y \right )= 20y\)

\(\displaystyle 4 (3y + 2y) = 4\left [ (3 + 2) y \right ] = 4\left ( 5y\right ) = 20y\)

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