ISEE Upper Level Quantitative : How to multiply exponents

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

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Example Questions

Example Question #101 : Numbers And Operations

Simplify: \displaystyle \left (y ^{3} \right )^{4}

Possible Answers:

\displaystyle y ^{7}

\displaystyle y ^{12}

The correct answer is not among the other choices.

\displaystyle y ^{64}

\displaystyle y ^{81}

Correct answer:

\displaystyle y ^{12}

Explanation:

Apply the power of a power property:

\displaystyle \left (y ^{3} \right )^{4} = y ^{3 \cdot 4} = y^{12}

Example Question #2 : Exponential Operations

Simplify the expression: \displaystyle \left (5 a^{3}y ^{4} \right )^{2}

Possible Answers:

\displaystyle 25a^{6} y^{8}

\displaystyle 25a^{9} y^{16}

\displaystyle 10a^{6} y^{8}

\displaystyle 10a^{9} y^{16}

\displaystyle 10a^{5} y^{6}

Correct answer:

\displaystyle 25a^{6} y^{8}

Explanation:

Apply the power of a product rule, then apply the power of a power rule:

\displaystyle \left (5 a^{3}y ^{4} \right )^{2}

\displaystyle = 5^{2} \cdot \left (a^{3}\right )^{2} \cdot \left ( y ^{4} \right )^{2}

\displaystyle = 25 \cdot a^{ 3 \cdot 2 } \cdot y ^{ 4 \cdot 2 }

\displaystyle = 25 a^{ 6} y ^{ 8 }

Example Question #1 : How To Multiply Exponents

Which of the following expressions is equal to \displaystyle 1,234^{0} ?

Possible Answers:

\displaystyle 1

The expression is undefined.

\displaystyle 1,234

\displaystyle 0

\displaystyle \frac{1}{1,234 }

Correct answer:

\displaystyle 1

Explanation:

Any nonzero number raised to the power of 0 is equal to 1.

Example Question #1 : How To Multiply Exponents

Which quantity is greater?

(a) \displaystyle (-5) ^{3}

(b) \displaystyle (-5) ^{-3}

Possible Answers:

(b) is greater.

(a) is greater.

It is impossible to tell from the information given.

(a) and (b) are equal.

Correct answer:

(b) is greater.

Explanation:

(a) \displaystyle (-5) ^{3} = (-5) \cdot (-5) \cdot (-5) = 25 \cdot (-5) = -125

(b) \displaystyle (-5) ^{-3} = \frac{1}{(-5) ^{3}} = \frac{1}{-125} =- \frac{1}{125}

(b) is the greater quantity.

Example Question #104 : Numbers And Operations

\displaystyle x is positive.

Which is the greater quantity?

(a) \displaystyle 100 ^{2x}

(b) \displaystyle 1,000 ^{x}

Possible Answers:

It is impossible to tell from the information given

(a) and (b) are equal

(a) is greater

(b) is greater

Correct answer:

(a) is greater

Explanation:

Use the power of a power property:

(a) \displaystyle 100 ^{2x} = \left (10^{2} \right ) ^{2x} = 10^{2\cdot 2x }= 10^{4x }

(b) \displaystyle 1,000 ^{x} =\left ( 1 0 ^{3} \right ) ^{x} = 1 0 ^{3x}

Since \displaystyle x > 0\displaystyle 4x > 3x. Subsequently, 

\displaystyle 100 ^{2x} = 10^{4x } > 10^{3x } = 1,000^{x },

making (a) greater

Example Question #5 : How To Multiply Exponents

Which is the greater quantity?

(a) \displaystyle 2 ^{100}

(b) \displaystyle 4^{50}

Possible Answers:

(a) is greater

(b) is greater

(a) and (b) are equal

It is impossible to tell from the information given

Correct answer:

(a) and (b) are equal

Explanation:

\displaystyle 4^{50} = \left ( 2 ^{2} \right )^{50} = 2 ^{ 2\; \cdot \;50 } = 2 ^{ 100 }

The two quantities are equal. 

Example Question #1 : How To Multiply Exponents

Two quantities are given - one in Column A and the other in Column B. Compare the quantities in the two columns.

Assume, in both columns, that \displaystyle x\neq0.

Column A                    Column B

\displaystyle x^{4}\cdot x^2                           \displaystyle \frac{x^{11}}{x^{2}}

Possible Answers:

The quantity in Column B is greater.

The quantities in both columns are equal.

The quantity in Column A is greater.

There is no way to determine the relationship between the columns.

Correct answer:

There is no way to determine the relationship between the columns.

Explanation:

Column A gives simplifies to give us \displaystyle \ x^{6}, and Column B simplifies to give us \displaystyle x^{9}. At first glance, Column B is greater, as it would be for all answers greater than 1. However, if \displaystyle x=1, the two columns are equal. Furthermore, if \displaystyle x is negative, or a fraction, Column A is greater. Thus, since we could arrive at all three answers by using different numbers, we cannot determine the answer conclusively.

Example Question #8 : How To Multiply Exponents

Which of the following expressions is equivalent to 

\displaystyle \left (\sqrt{1,001}-\sqrt{999} \right ) \left ( \sqrt{1,001}+\sqrt{999} \right ) ?

Possible Answers:

\displaystyle \sqrt{2}

\displaystyle 20\sqrt{5}

\displaystyle 2

\displaystyle 2,000

\displaystyle 2,000 - 3 \sqrt{111,111}

Correct answer:

\displaystyle 2

Explanation:

Use the difference of squares pattern as follows:

\displaystyle \left (\sqrt{1,001}-\sqrt{999} \right ) \left ( \sqrt{1,001}+\sqrt{999} \right )

\displaystyle = \left (\sqrt{1,001} \right ) ^{2} - \left (\ \sqrt{999} \right ) ^{2}

\displaystyle =1,001 - 999 = 2

Example Question #1 : Exponents

Column A                  Column B

\displaystyle \left ( \frac{5x^2}{25y^4} \right )^{0}                   \displaystyle 0

Possible Answers:

The quantity in Column B is greater.

The quantity in Column A is greater.

The quantities in both columns are equal.

No relationship between the columns can be determined.

Correct answer:

The quantity in Column A is greater.

Explanation:

Anything raised to zero is equal to 1. Therefore, Column A has to be greater because 1 is greater than 0.

Example Question #2 : Exponents

44,000,000 can be written in scientific notation as \displaystyle a \times 10 ^{N} for some \displaystyle a, N.

Which is the greater quantity?

(A) \displaystyle N

(B) 8

Possible Answers:

(A) is greater

It is impossible to determine which is greater from the information given

(A) and (B) are equal

(B) is greater

Correct answer:

(B) is greater

Explanation:

To write 44,000,000 in scientifc notation, write the implied decimal point after the final "0", then move it left until it is after the first nonzero digit (the first "4").

\displaystyle 44 000 000. \Rightarrow 4.4 000 000

This requires a displacement of seven places, so  

\displaystyle 44,000,000 = 4.4 \times 10^{7}

\displaystyle N = 7 < 8, and (B) is greater.

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