ISEE Upper Level Quantitative : Variables

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

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Example Questions

Example Question #2 : How To Divide Exponential Variables

Simplify: 

\displaystyle \frac{10 x ^{-6} y ^{-4}}{20x ^{-8}y^{-2}}

Possible Answers:

\displaystyle \frac{2}{x ^{2}y ^{2} }

\displaystyle \frac{1 }{2 x ^{2}y ^{2}}

\displaystyle \frac{x ^{2} }{2y ^{2} }

\displaystyle \frac{x ^{2}y ^{2} }{2 }

\displaystyle \frac{y ^{2} }{2x ^{2} }

Correct answer:

\displaystyle \frac{x ^{2} }{2y ^{2} }

Explanation:

Break the fraction up and apply the quotient of powers rule:

\displaystyle \frac{10 x ^{-6} y ^{-4}}{20x ^{-8}y^{-2}}

\displaystyle = \frac{10 }{20} \cdot \frac{ x ^{-6} }{x ^{-8}} \cdot \frac{y ^{-4}}{y^{-2}}

\displaystyle = \frac{1 }{2} \cdot x ^{-6- (-8)} \cdot y ^{-4- (-2)}

\displaystyle = \frac{1 }{2} \cdot x ^{2} \cdot y ^{-2}

\displaystyle = \frac{1 }{2} \cdot x ^{2} \cdot \frac{1}{y ^{2}}

\displaystyle = \frac{x ^{2} }{2y ^{2} }

Example Question #261 : Algebraic Concepts

Simplify: \displaystyle \frac{16x^4}{12x^2}

Possible Answers:

\displaystyle \frac{4}{3}

\displaystyle 16x

\displaystyle \frac{x^2}{3}

\displaystyle \frac{4}{3x^2}

\displaystyle \frac{4x^2}{3}

Correct answer:

\displaystyle \frac{4x^2}{3}

Explanation:

To simplify this expression, look at the like terms separately. First, simplify \displaystyle \frac{16}{12}. This becomes \displaystyle \frac{4}{3}. Then, deal with the \displaystyle \frac{x^4}{x^2}. Since the bases are the same and you're dividing, you can subtract exponents. This gives you \displaystyle x^2. Since the exponent is positive, you put in the numerator. This gives you a final answer of \displaystyle \frac{4x^2}{3}.

Example Question #5 : How To Divide Exponential Variables

\displaystyle x is a negative number.

Which is the greater quantity?

(a) The reciprocal of \displaystyle x^{7}

(b) The reciprocal of \displaystyle x^{8}

Possible Answers:

(b) is the greater quantity

(a) and (b) are equal

(a) is the greater quantity

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

Correct answer:

(b) is the greater quantity

Explanation:

A negative number raised to an odd power is negative; a negative number raised to an even power is positive. It follows that \displaystyle x^{7} is negative and \displaystyle x^{8} is positive. Also, the reciprocal of a nonzero number assumes the same sign as the number itself, so the reciprocal of \displaystyle x^{8} is positive and that of \displaystyle x^{7} is negative. It follows that the reciprocal of \displaystyle x^{8} is the greater of the two.

Example Question #2 : How To Divide Exponential Variables

Simplify: 

\displaystyle \frac{10 x ^{-6} y ^{-4}}{20x ^{-8}y^{-2}}

Possible Answers:

\displaystyle \frac{y ^{2} }{2x ^{2} }

\displaystyle \frac{2}{x ^{2}y ^{2} }

\displaystyle \frac{x ^{2} }{2y ^{2} }

\displaystyle \frac{x ^{2}y ^{2} }{2 }

\displaystyle \frac{1 }{2 x ^{2}y ^{2}}

Correct answer:

\displaystyle \frac{x ^{2} }{2y ^{2} }

Explanation:

Break the fraction up and apply the quotient of powers rule:

\displaystyle \frac{10 x ^{-6} y ^{-4}}{20x ^{-8}y^{-2}}

\displaystyle = \frac{10 }{20} \cdot \frac{ x ^{-6} }{x ^{-8}} \cdot \frac{y ^{-4}}{y^{-2}}

\displaystyle = \frac{1 }{2} \cdot x ^{-6- (-8)} \cdot y ^{-4- (-2)}

\displaystyle = \frac{1 }{2} \cdot x ^{2} \cdot y ^{-2}

\displaystyle = \frac{1 }{2} \cdot x ^{2} \cdot \frac{1}{y ^{2}}

\displaystyle = \frac{x ^{2} }{2y ^{2} }

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