ACT Math : Exponents

Study concepts, example questions & explanations for ACT Math

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Example Questions

Example Question #111 : Exponents

If , then  ?

Possible Answers:

15

4

5

25

10

Correct answer:

5

Explanation:

 

Calculate the power of  that makes the expression equal to 25. We can set up an alternate or equivalent equation to solve this problem:

Solve this equation by taking the square root of both sides. 

, because logarithmic equations cannot have a negative base.

The solution to this expression is:

 

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

If  and , then which of the following CANNOT be the value of ?

 

Possible Answers:

Correct answer:

Explanation:

Even roots of numbers can either be positive or negative. Thus, x = +/- 5 and y = +/- 3. The possible values from x + y can therefore be:

(-5) + (-3) = -8

(-5) + 3 = -2

5 + (-3) = 2

5 + 3 = 8

Example Question #2 : How To Find A Ratio Of Exponents

If  for all \dpi{100} \small n not equal to 0, which of the following must be true?

Possible Answers:

\dpi{100} \small \frac{x}{y} = 6

\dpi{100} \small \frac{y}{x} = 6

\dpi{100} \small y-x = 6

\dpi{100} \small y+x = 6

\dpi{100} \small yx = 6

Correct answer:

\dpi{100} \small y-x = 6

Explanation:

Remember that \dpi{100} \small \frac{n^{y}}{n^{x}}=n^{y-x}

Since the problem states that , you can assume that \dpi{100} \small n^{y-x}=n^{6}

This shows that \dpi{100} \small y-x = 6.

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

If  and are positive integers and , then what is the value of ?

Possible Answers:

Correct answer:

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 #2 : How To Find A Ratio Of Exponents

Write the following logarithm in expanded form:

 

Possible Answers:

Correct answer:

Explanation:

Example Question #2 : How To Find A Ratio Of Exponents

If  and  are both rational numbers and , what is ?

Possible Answers:

Correct answer:

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.

And, would you look at that. .  Therefore, .

Example Question #1 : How To Find The Square Of Difference

can be rewritten as:

Possible Answers:

Correct answer:

Explanation:

Use the formula for solving the square of a difference, . In this case, 

Example Question #1 : Squaring / Square Roots / Radicals

Expand:

Possible Answers:

Correct answer:

Explanation:

To multiply a difference squared, square the first term and add two times the multiplication of the two terms. Then add the second term squared.

Example Question #2 : Squaring / Square Roots / Radicals

The expression   is equivalent to:

Possible Answers:

Correct answer:

Explanation:

First, we need to factor the numerator and denominator separately and cancel out similar terms. We will start with the numerator because it can be factored easily as the difference of two squares. 

  

Now factor the quadratic in the denominator.

Substitute these factorizations back into the original expression.

The  terms cancel out, leaving us with the following answer:

Example Question #1 : Squaring / Square Roots / Radicals

Evaluate the following expression:

Possible Answers:

Correct answer:

Explanation:

2 raised to the power of 5 is the same as multiplying 2 by itself 5 times so:

25 = 2x2x2x2x2 = 32

Then, 5x2 must first be multiplied before taking the exponent, yielding 102 = 100.

100 + 32 = 132

 

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