ACT Math : Exponents

Study concepts, example questions & explanations for ACT Math

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Example Questions

Example Question #41 : Exponents

Simplify: hn + h–2n 

Possible Answers:

\displaystyle 2h^{-n}

\displaystyle h^n+\frac{1}{h^{2n}}

\displaystyle h

\displaystyle \frac{h^n}{h^{2n}}

\displaystyle h^{-n}

Correct answer:

\displaystyle h^n+\frac{1}{h^{2n}}

Explanation:

h–2n = 1/h2n

hn + h–2n = hn + 1/h2n

Example Question #42 : Exponents

Simplify: 3y2 + 7y2 + 9y3 – y3 + y 

Possible Answers:

10y4 + 8y6 + y

10y2 + 10y3 + y

10y2 + 8y3 + y

10y2 + 9y3

19y11

Correct answer:

10y2 + 8y3 + y

Explanation:

Add the coefficients of similar variables (y, y2, 9y3)

3y2 + 7y2 + 9y3 – y3 + y =

(3 + 7)y2 + (9 – 1)y3 + y =

10y2 + 8y3 + y

Example Question #43 : Exponents

Simplify the following:

\displaystyle \frac{K^3K^4}{M^6M^2}

 

Possible Answers:

\displaystyle \frac{K^{-1}}{M^4}

\displaystyle \frac{KM^{\frac{1}{2}}}{KM^{\frac{1}{2}}}

\displaystyle \frac{K^8}{M^7}

\displaystyle \frac{K^7}{M^8}

\displaystyle \frac{K^{12}}{M^{12}}

Correct answer:

\displaystyle \frac{K^7}{M^8}

Explanation:

When common variables have exponents that are multiplied, their exponents are added. So K* K4 =K(3+4) = K7.  And M6 * M2 = M(6+2) = M8. So the answer is K7/M8.

Example Question #44 : Exponents

Solve for \displaystyle x:

\displaystyle \frac{64^4}{8^x} = 8

Possible Answers:

\displaystyle x=-7

\displaystyle x=7

\displaystyle x=1

\displaystyle x=0

\displaystyle x=8

Correct answer:

\displaystyle x=7

Explanation:

First, reduce all values to a common base using properties of exponents.

\displaystyle 64^4 = (8^2)^4 = 8^8

Plugging back into the equation-

\displaystyle 8^8 = 8^x\cdot 8^1

Using the formula 

\displaystyle x^a\cdot x^b=x ^{a+b}

We can reduce our equation to 

\displaystyle x +1 = 8

So,

\displaystyle x = 7

Example Question #45 : Exponents

Simplify:  y3x4(yx3 + y2x2 + y15 + x22)

Possible Answers:

y4x7 + y5x6 + y18x4 + y3x26

y3x12 + y6x8 + y45 + x88

y3x12 + y6x8 + y45x4 + y3x88

y3x12 + y12x8 + y24x4 + y3x23

2x4y4 + 7y15 + 7x22

Correct answer:

y4x7 + y5x6 + y18x4 + y3x26

Explanation:

When you multiply exponents, you add the common bases:

y4 x7 + y5x6 + y18x4 + y3x26

Example Question #1 : Exponential Operations

If \displaystyle \frac{3^{y - 1}}{3^{-2}} = 27^{y}3^{y}, what is the value of \displaystyle y?

Possible Answers:

\displaystyle \frac{3}{2}

\displaystyle 3

\displaystyle \frac{2}{3}

\displaystyle \frac{1}{3}

\displaystyle 4

Correct answer:

\displaystyle \frac{1}{3}

Explanation:

Rewrite the term on the left as a product. Remember that negative exponents shift their position in a fraction (denominator to numerator).

\displaystyle 3^{y-1}*3^2=27^y3^y

The term on the right can be rewritten, as 27 is equal to 3 to the third power.

\displaystyle 3^{y-1}*3^2=(3^3)^y*3^y

Exponent rules dictate that multiplying terms allows us to add their exponents, while one term raised to another allows us to multiply exponents.

\displaystyle 3^{(y-1)+2}=(3)^{3y}*3^y

\displaystyle 3^{y+1}=3^{3y+y}=3^{4y}

We now know that the exponents must be equal, and can solve for \displaystyle y.

\displaystyle y+1=4y

\displaystyle 1=3y

\displaystyle \frac{1}{3}=y

 

Example Question #2 : How To Add Exponents

If \displaystyle 5^2 \times 5^n = 5^{12}, what is the value of \displaystyle n?

Possible Answers:

\displaystyle 4

\displaystyle 10

\displaystyle 24

\displaystyle 14

\displaystyle 6

Correct answer:

\displaystyle 10

Explanation:

Since the base is 5 for each term, we can say 2 + n =12.  Solve the equation for n by subtracting 2 from both sides to get n = 10.

Example Question #2233 : Act Math

Which expression is equivalent to the following? \displaystyle 2^2 + 2^2 + 2^3

Possible Answers:

\displaystyle 2^{12}

None of these

\displaystyle 2^7

\displaystyle 4^2 + 2^3

\displaystyle 6^7

Correct answer:

None of these

Explanation:

The rule for adding exponents is \displaystyle a^m \cdot a^n = a^{m+n}. We can thus see that \displaystyle 2^2 and \displaystyle 2^3 are no more compatible for addition than \displaystyle x^2 and \displaystyle x^3 are.

You could combine the first two terms into \displaystyle 2(2^2), but note that PEMDAS prevents us from equating this to \displaystyle 4^2 (the exponent must solve before the distribution).

Example Question #2234 : Act Math

Express as a power of 2: \displaystyle 2(4^3) \cdot 4(2^3)

Possible Answers:

\displaystyle 2^{12}

\displaystyle 2^{16}

The expression cannot be rephrased as a power of 2.

\displaystyle 2^7

\displaystyle 2^{22}

Correct answer:

\displaystyle 2^{12}

Explanation:

Since the problem requires us to finish in a power of 2, it's easiest to begin by reducing all terms to powers of 2. Fortunately, we do not need to use logarithms to do so here.

\displaystyle 2(4^3) = 2^1((2^2)^3)

\displaystyle 4(2^3) = 2^2(2^3)

Thus, \displaystyle 2(4^3) \cdot 4(2^3) = 2^1((2^2)^3) \cdot 2^2(2^3) = 2^1(2^6) \cdot (2^5) = 2^7 \cdot 2^5 = 2^{12}

Example Question #46 : Exponents

Simplify the following expression:
\displaystyle x^3*x^5*y^2*y^7

Possible Answers:

\displaystyle x*y^{17}

\displaystyle (x*y)^{17}

\displaystyle (x*y)^{210}

\displaystyle x^8*y^9

\displaystyle x^{15}*y^{14}

Correct answer:

\displaystyle x^8*y^9

Explanation:

When multiplying bases that have exponents, simply add the exponents. Note that you can only add the exponents if the bases are the same. Thus:

\displaystyle x^3*x^5*y^2*y^7 \displaystyle = x^{3+5}*y^{2+7} = x^8*y^9

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