PSAT Math : Exponents

Study concepts, example questions & explanations for PSAT Math

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Example Questions

Example Question #1 : How To Add Exponents

If a2 = 35 and b2 = 52 then a4 + b6 = ?

Possible Answers:

3929

141,833

150,000

140,608

522

Correct answer:

141,833

Explanation:

a4 = a2 * a2  and  b6= b2 * b* b2

Therefore a4 + b6 = 35 * 35 + 52 * 52 * 52 = 1,225 + 140,608 = 141,833

Example Question #1 : Exponential Operations

If \(\displaystyle 9^{(x + 5)}+3^{2(x+5)}=162\), what is the value of \(\displaystyle x\)?

Possible Answers:

\(\displaystyle 0\)

\(\displaystyle -3\)

\(\displaystyle -1\)

\(\displaystyle 1\)

Correct answer:

\(\displaystyle -3\)

Explanation:

Since we have two \(\displaystyle x\)’s in \(\displaystyle 9^{(x + 5)} + 3^{2(x + 5)}\) we will need to combine the two terms.

For \(\displaystyle 3^{2(x + 5) }\) this can be rewritten as

\(\displaystyle (3^2)^{ (x + 5)} = 9^ {(x + 5)}\)

So we have \(\displaystyle 9^{ (x + 5) }+ 9^{ (x + 5)} = 162\).

Or \(\displaystyle 2 (9^{ (x + 5)}) = 162\)

Divide this by \(\displaystyle 2\)\(\displaystyle 9^{ (x + 5)} = 81 = 9^ 2\)

Thus \(\displaystyle x +5 = 2\) or \(\displaystyle x = -3\)

*Hint: If you are really unsure, you could have plugged in the numbers and found that the first choice worked in the equation.

Example Question #3 : How To Add Exponents

Solve for x. 

2+ 2x+1 = 72

Possible Answers:

7

5

3

6

4

Correct answer:

5

Explanation:

The answer is 5. 

8 + 2x+1 = 72

      2x+1 = 64

      2x+1 = 26

      x + 1 = 6

           x = 5

Example Question #4 : How To Add Exponents

Which of the following is eqivalent to 5b – 5(b–1) – 5(b–1) – 5(b–1) – 5(b–1) – 5(b–1) , where b is a constant?

Possible Answers:

1

5

5b–1

0

1/5

Correct answer:

0

Explanation:

We want to simplify 5b – 5(b–1) – 5(b–1) – 5(b–1) – 5(b–1) – 5(b–1) .

Notice that we can collect the –5(b–1) terms, because they are like terms. There are 5 of them, so that means we can write –5(b–1) – 5(b–1) – 5(b–1) – 5(b–1) – 5(b–1) as (–5(b–1))5.

To summarize thus far:

5b – 5(b–1) – 5(b–1) – 5(b–1) – 5(b–1) – 5(b–1) = 5b +(–5(b–1))5

It's important to interpret –5(b–1) as (–1)5(b–1) because the –1 is not raised to the (b – 1) power along with the five. This means we can rewrite the expression as follows:

5b +(–5(b–1))5 = 5b + (–1)(5(b–1))(5) = 5b – (5(b–1))(5)

Notice that 5(b–1) and 5 both have a base of 5. This means we can apply the property of exponents which states that, in general, abac = ab+c. We can rewrite 5 as 51 and then apply this rule.

5b – (5(b–1))(5) = 5b – (5(b–1))(51) = 5b – 5(b–1+1)

Now, we will simplify the exponent b – 1 + 1 and write it as simply b.

5b – 5(b–1+1) = 5b – 5b = 0

The answer is 0.

Example Question #481 : Algebra

Ifx^2=11\(\displaystyle x^2=11\), then what does x^4\(\displaystyle x^4\) equal?

Possible Answers:

\(\displaystyle 22\)

\(\displaystyle 44\)

\(\displaystyle 144\)

\(\displaystyle 121\)

\(\displaystyle 110\)

Correct answer:

\(\displaystyle 121\)

Explanation:

\(\displaystyle x^4=(x^2)(x^2)=11\cdot 11=121\)

Example Question #6 : How To Add Exponents

Simplify.  All exponents must be positive.

\left ( x^{-2}y^{3} \right )\left ( x^{5}y^{-4} \right )\(\displaystyle \left ( x^{-2}y^{3} \right )\left ( x^{5}y^{-4} \right )\)

Possible Answers:

\(\displaystyle x^{2}y^{7}\)

\left ( x^{-2}+x^{5} \right )\left ( y^{3}+y^{-4} \right )\(\displaystyle \left ( x^{-2}+x^{5} \right )\left ( y^{3}+y^{-4} \right )\)

\(\displaystyle x^{7}y^{7}\)

\(\displaystyle \frac{x^{3}}{y}\)

\(\displaystyle x^{3}y^{-2}\)

Correct answer:

\(\displaystyle \frac{x^{3}}{y}\)

Explanation:

Step 1: \left ( x^{-2}x^{5} \right )= x^{3}\(\displaystyle \left ( x^{-2}x^{5} \right )= x^{3}\)

Step 2: \left ( y^{3}y^{-4} \right )= y^{-1}= \frac{1}{y}\(\displaystyle \left ( y^{3}y^{-4} \right )= y^{-1}= \frac{1}{y}\)

Step 3: (Correct Answer): \frac{x^{3}}{y}\(\displaystyle \frac{x^{3}}{y}\)

Example Question #7 : How To Add Exponents

Simplify.  All exponents must be positive.

\(\displaystyle \frac{x^{-3}y^{5}}{x^{2}y^{-1}}\)

Possible Answers:

\frac{y^{6}}{x^{5}}\(\displaystyle \frac{y^{6}}{x^{5}}\)

x^{-1}y^{4}\(\displaystyle x^{-1}y^{4}\)

x^{-5}y^{6}\(\displaystyle x^{-5}y^{6}\)

\frac{1}{x^{5}y^{-6}}\(\displaystyle \frac{1}{x^{5}y^{-6}}\)

\frac{\left ( xy \right )^{2}}{\left ( xy \right )}\(\displaystyle \frac{\left ( xy \right )^{2}}{\left ( xy \right )}\)

Correct answer:

\frac{y^{6}}{x^{5}}\(\displaystyle \frac{y^{6}}{x^{5}}\)

Explanation:

Step 1: \frac{y^{5}}{\left ( x^{3}x^{2} \right )\left \right )y^{-1}}\(\displaystyle \frac{y^{5}}{\left ( x^{3}x^{2} \right )\left \right )y^{-1}}\)

 

Step 2: \frac{\left ( y^{5}y^{1} \right )}{x^{3}x^{2}}\(\displaystyle \frac{\left ( y^{5}y^{1} \right )}{x^{3}x^{2}}\)

Step 3:\frac{y^{6}}{x^{5}}\(\displaystyle \frac{y^{6}}{x^{5}}\)

Example Question #8 : How To Add Exponents

\frac{\left ( -11 \right )^{-8}}{\left ( -11\right )^{12}}\(\displaystyle \frac{\left ( -11 \right )^{-8}}{\left ( -11\right )^{12}}\)

Answer must be with positive exponents only.

Possible Answers:

\frac{1}{\left ( -11 \right )^{4}}\(\displaystyle \frac{1}{\left ( -11 \right )^{4}}\)

\left ( -11 \right )^{-20}\(\displaystyle \left ( -11 \right )^{-20}\)

\frac{1}{\left ( -11 \right )^{20}}\(\displaystyle \frac{1}{\left ( -11 \right )^{20}}\)

\left ( -11 \right )^{4}\(\displaystyle \left ( -11 \right )^{4}\)

\left ( 1 \right )^{-20}\(\displaystyle \left ( 1 \right )^{-20}\)

Correct answer:

\frac{1}{\left ( -11 \right )^{20}}\(\displaystyle \frac{1}{\left ( -11 \right )^{20}}\)

Explanation:

Step 1:\frac{1}{\left ( -11 \right )^{12}\left ( -11 \right )^{8}}\(\displaystyle \frac{1}{\left ( -11 \right )^{12}\left ( -11 \right )^{8}}\)

Step 2: The above is equal to \frac{1}{\left ( -11 \right )^{20}}\(\displaystyle \frac{1}{\left ( -11 \right )^{20}}\)

Example Question #482 : Algebra

Evaluate:

 -\left ( -3 \right )^{0}-\left ( -3^{0} \right )\(\displaystyle -\left ( -3 \right )^{0}-\left ( -3^{0} \right )\)

Possible Answers:

\(\displaystyle 6\)

\(\displaystyle 2\)

\(\displaystyle -1\)

\(\displaystyle 0\)

\(\displaystyle 1\)

Correct answer:

\(\displaystyle 0\)

Explanation:

-\left ( -3 \right )^{0}= -1\(\displaystyle -\left ( -3 \right )^{0}= -1\)

\(\displaystyle (-3^{0})=-1\)

 \(\displaystyle -1-(-1)=-1+1=0\)

Example Question #10 : How To Add Exponents

Simplify:

\(\displaystyle 3\sqrt{18} + 2\sqrt{50}\)

Possible Answers:

\(\displaystyle 10\sqrt{2}\)

\(\displaystyle 19\sqrt{2}\)

\(\displaystyle 5\sqrt{68}\)

\(\displaystyle 9\sqrt{2}\)

\(\displaystyle None\ of\ the\ above\)

Correct answer:

\(\displaystyle 19\sqrt{2}\)

Explanation:

\(\displaystyle 3\sqrt{18} = 3\sqrt{2\star 3^{2}} = 9\sqrt{2}\)

Similarly \(\displaystyle 2\sqrt{50} = 2\sqrt{2\star 5^{2}} = 10\sqrt{2}\)

 

So \(\displaystyle 9\sqrt{2} + 10\sqrt{2}= 19\sqrt{2}\)

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