PSAT Math : How to add exponents

Study concepts, example questions & explanations for PSAT Math

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Example Questions

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Example Question #11 : Exponential Operations

If , what is the value of ?

Possible Answers:

Correct answer:

Explanation:

Using exponents, 27 is equal to 33. So, the equation can be rewritten:

34+ 6 = (33)2x

34+ 6 = 36x

When both side of an equation have the same base, the exponents must be equal. Thus:

4x + 6 = 6x

6 = 2x

x = 3

Example Question #81 : Exponents

What is the value of  such that ?

Possible Answers:

Correct answer:

Explanation:

We can solve by converting all terms to a base of two. 4, 16, and 32 can all be expressed in terms of 2 to a standard exponent value.

We can rewrite the original equation in these terms.

Simplify exponents.

Finally, combine terms.

From this equation, we can see that .

Example Question #11 : Exponents

How many of the following base ten numbers have a base five representation of exactly four digits?

(A) 

(B) 

(C) 

(D) 

Possible Answers:

Four

None

One

Two

Three

Correct answer:

Three

Explanation:

A number in base five has powers of five as its place values; starting at the right, they are 

The lowest base five number with four digits would be

 in base ten.

The lowest base five number with five digits would be

 in base ten.

Therefore, a number that is expressed as a four-digit number in base five must fall in the range

Three of the four numbers - all except 100 - fall in this range.

Example Question #11 : Exponents

Solve for x:

Possible Answers:

9

6

8

11

10

Correct answer:

10

Explanation:

Combining the powers, we get 1024=2^{x}.

From here we can use logarithms, or simply guess and check to get x=10.

Example Question #11 : Exponents

If \dpi{100} \small r and \dpi{100} \small s are positive integers, and \dpi{100} \small 25\left ( 5^{r} \right )=5^{s-2}, then what is \dpi{100} \small s in terms of \dpi{100} \small r?

Possible Answers:

\dpi{100} \small r+4

\dpi{100} \small r

\dpi{100} \small r+3

\dpi{100} \small r+1

\dpi{100} \small r+2

Correct answer:

\dpi{100} \small r+4

Explanation:

\dpi{100} \small 25\left ( 5^{r} \right ) is equal to  which is equal to \dpi{100} \small \left ( 5^{r+2} \right ). If we compare this to the original equation we get \dpi{100} \small r+2=s-2\rightarrow s=r+4

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