SAT Math : How to find patterns in exponents

Study concepts, example questions & explanations for SAT Math

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Example Questions

Example Question #1 : Pattern Behaviors In Exponents

If ax·a4 = a12 and (by)3 = b15, what is the value of x - y?

Possible Answers:

-9

6

3

-2

-4

Correct answer:

3

Explanation:

Multiplying like bases means add the exponents, so x+4 = 12, or x = 8.

Raising a power to a power means multiply the exponents, so 3y = 15, or y = 5.

x - y = 8 - 5 = 3.

Example Question #1 : How To Find Patterns In Exponents

If p and q are positive integrers and 27= 9q, then what is the value of q in terms of p?

Possible Answers:

3p

2p

p

(2/3)p

(3/2)p

Correct answer:

(3/2)p

Explanation:

The first step is to express both sides of the equation with equal bases, in this case 3. The equation becomes 33p = 32q. So then 3p = 2q, and q = (3/2)p is our answer. 

Example Question #3 : How To Find Patterns In Exponents

Simplify 272/3.

Possible Answers:

3

125

9

729

27

Correct answer:

9

Explanation:

272/3 is 27 squared and cube-rooted. We want to pick the easier operation first. Here that is the cube root. To see that, try both operations. 

272/3 = (272)1/3 = 7291/3 OR

272/3 = (271/3)2 = 32

Obviously 32 is much easier. Either 32 or 7291/3 will give us the correct answer of 9, but with 32 it is readily apparent. 

Example Question #3 : Pattern Behaviors In Exponents

If \displaystyle a and \displaystyle b are integers and 

\displaystyle \left ( \frac{1}{3} \right )^{a}=27^{b} 

what is the value of \displaystyle a\div b? 

Possible Answers:

\displaystyle -3

\displaystyle 9

\displaystyle 3

\displaystyle -\frac{1}{3}

\displaystyle \frac{1}{3}

Correct answer:

\displaystyle -3

Explanation:

To solve this problem, we will have to take the log of both sides to bring down our exponents. By doing this, we will get \dpi{100} \small a\ast log\left (\frac{1}{3} \right )= b\ast log\left ( 27 \right ).

To solve for \dpi{100} \small \frac{a}{b} we will have to divide both sides of our equation by \dpi{100} \small log\frac{1}{3} to get \dpi{100} \small \frac{a}{b}=\frac{log\left ( 27 \right )}{log\left ( \frac{1}{3} \right )}.

\dpi{100} \small \frac{log\left ( 27 \right )}{log\left ( \frac{1}{3} \right )} will give you the answer of –3.

Example Question #2441 : Sat Mathematics

If\displaystyle \log 2=0.301 and \displaystyle \log 3=0.477, then what is \displaystyle \log 12?

Possible Answers:

\displaystyle 1.346

\displaystyle 1.592

\displaystyle 1.255

\displaystyle 1.116

\displaystyle 1.079

Correct answer:

\displaystyle 1.079

Explanation:

We use two properties of logarithms: 

log(xy) = log (x) + log (y)\displaystyle log(xy) = log (x) + log (y)

log(x^{n}) = nlog (x)\displaystyle log(x^{n}) = nlog (x)

So \displaystyle \log 12=2 \log2+\log3

Example Question #2442 : Sat Mathematics

Evaluate:

x^{-3}x^{6}\displaystyle x^{-3}x^{6}

Possible Answers:

x^{-3}\displaystyle x^{-3}

x^{9}\displaystyle x^{9}

x^{-18}\displaystyle x^{-18}

x^{3}\displaystyle x^{3}

x^{6}\displaystyle x^{6}

Correct answer:

x^{3}\displaystyle x^{3}

Explanation:

x^{m}\ast x^{n} = x^{m + n}\displaystyle x^{m}\ast x^{n} = x^{m + n}, here \displaystyle m=-3 and \displaystyle n=6, hence \displaystyle -3+6=3.

Example Question #7 : How To Find Patterns In Exponents

Solve for \displaystyle x

\left ( \frac{2}{3} \right )^{x+1} = \frac{27}{8}\displaystyle \left ( \frac{2}{3} \right )^{x+1} = \frac{27}{8}

Possible Answers:

None of the above

\displaystyle 2

\displaystyle -4

\displaystyle 4

\displaystyle -2

Correct answer:

\displaystyle -4

Explanation:

\left ( \frac{2}{3} \right )^{x+1} = \frac{27}{8}\displaystyle \left ( \frac{2}{3} \right )^{x+1} = \frac{27}{8} = \left ( \frac{3}{2} \right )^{3} = \left ( \frac{2}{3} \right )^{-3}\displaystyle \left ( \frac{3}{2} \right )^{3} = \left ( \frac{2}{3} \right )^{-3}

 \displaystyle x+1=-3 which means \displaystyle x=-4

Example Question #11 : Pattern Behaviors In Exponents

Which of the following statements is the same as:

\displaystyle I)\ 2^{2x+4-y} \quad II)\ 2^{x+2} / 4^y \quad III)\ (4^x)( 4^2 )(2^{-y} )

Possible Answers:

\displaystyle II \mbox{ and } III \mbox{ only}

\displaystyle I \mbox{ only}

\displaystyle I, II \mbox{ and } III

\displaystyle I \mbox{ and } II \mbox{ only}

\displaystyle I \mbox{ and } III \mbox{ only}

Correct answer:

\displaystyle I \mbox{ and } III \mbox{ only}

Explanation:

Remember the laws of exponents. In particular, when the base is nonzero:

\displaystyle b^{m+n} = b^m b^n \qquad (b^m)^n = b^{mn} \\ (b \times c)^n = b^n c^n \qquad b^{-n} = 1/b^n

An effective way to compare these statements, is to convert them all into exponents with base 2. The original statement becomes:

\displaystyle 4^{x+2} / 2^y = 4^{x+2} (2^{-y}) = (2^2)^{x+2} 2^{-y} = 2^{2(x+2) } 2^{-y} = 2^{2x+4-y}

This is identical to statement I. Now consider statement II:

\displaystyle 2^{x+2} / 4^y = 2^{x+2} ( 4^{-y} ) = 2^{x+2} ( 2^2 )^{-y} = 2^{x+2} 2^{-2y} = 2^{x+2-2y} \neq 2^{2x+4-y}

Therefore, statement II is not identical to the original statement. Finally, consider statement III:

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

which is also identical to the original statement. As a result, only I and III are the same as the original statement. 

Example Question #1 : How To Find Patterns In Exponents

Write in exponential form:

\displaystyle \sqrt[3]{\left ( x-1 \right )^{2}}

Possible Answers:

\displaystyle \left ( x-1 \right )^{3}

\displaystyle \left ( x-1 \right )

\displaystyle \left ( x-1 \right )^{2}

\displaystyle \left ( x-1 \right )^{\frac{2}{3}}

\displaystyle \left ( x-1 \right )^{\frac{3}{2}}

Correct answer:

\displaystyle \left ( x-1 \right )^{\frac{2}{3}}

Explanation:

Using properties of radicals e.g., \displaystyle \sqrt[m]{x^{n}} = x^{\frac{n}{m}}

we get \displaystyle \sqrt[3]{\left ( x-1 \right )^{2}} = \left ( x-1 \right )^{\frac{2}{3}}

Example Question #12 : Pattern Behaviors In Exponents

Write in exponential form:

\displaystyle \sqrt[3]{x^{5}}

Possible Answers:

\displaystyle x^{5-3}

\displaystyle x^{5}

\displaystyle x^{\frac{3}{5}}

\displaystyle x^{\frac{5}{3}}

\displaystyle x^{3}

Correct answer:

\displaystyle x^{\frac{5}{3}}

Explanation:

Properties of Radicals

\displaystyle \sqrt[]{x} = x^{\frac{1}{2}}

\displaystyle \sqrt[3]{x} = x^{\frac{1}{3}}

\displaystyle x^{\frac{5}{3}}

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