SAT Math : How to find a ratio of exponents

Study concepts, example questions & explanations for SAT Math

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Example Questions

Example Question #1 : How To Find A Ratio Of Exponents

If \(\displaystyle m\) and \(\displaystyle n\) are positive integers and \(\displaystyle 4^m=64^n\), then what is the value of \(\displaystyle \frac{m}{n}\)?

Possible Answers:

\(\displaystyle \frac{5}{3}\)

\(\displaystyle 16\)

\(\displaystyle 3\)

\(\displaystyle \frac{1}{3}\)

\(\displaystyle \frac{1}{16}\)

Correct answer:

\(\displaystyle 3\)

Explanation:

43 = 64

Alternatively written, this is 4(4)(4) = 64 or 43 = 641.

Thus, m = 3 and n = 1.

m/n = 3/1 = 3.

Example Question #115 : Exponents

Write the following logarithm in expanded form:

 

\(\displaystyle \log x^{2}y\)

Possible Answers:

\(\displaystyle 2\log x-\log y\)

\(\displaystyle \log x^{2}+\log y\)

\(\displaystyle 2\log x+\log y\)

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

\(\displaystyle 2\left ( \log xy \right )\)

Correct answer:

\(\displaystyle 2\log x+\log y\)

Explanation:

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

Example Question #22 : Exponents

If \(\displaystyle m\) and \(\displaystyle n\) are both rational numbers and \(\displaystyle 4^{m} = 8^{n}\), what is \(\displaystyle \frac{m}{n}\)?

Possible Answers:

\(\displaystyle \frac{2}{1}\)

\(\displaystyle \frac{5}{3}\)

\(\displaystyle \frac{4}{1}\)

\(\displaystyle \frac{3}{2}\)

Correct answer:

\(\displaystyle \frac{3}{2}\)

Explanation:

This question is asking you for the ratio of m to n.  To figure it out, the easiest way is to figure out when 4 to an exponent equals 8 to an exponent.  The easiest way to do that is to list the first few results of 4 to an exponent and 8 to an exponent and check to see if any match up, before resorting to more drastic means of finding a formula.

\(\displaystyle 4^{1} = 4, 4^{2} = 16, 4^{3} = 64, 4^{4} = 256, 4^{5} = 1024\)

\(\displaystyle 8^{1}=8, 8^{2} = 64, 8^{3} = 512, 8^{4} = 4096, 8^{5} = 32768\)

And, would you look at that. \(\displaystyle 4^{3}= 8^{2}\).  Therefore, \(\displaystyle \frac{m}{n} = \frac{3}{2}\).

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