ACT Math : Exponents

Study concepts, example questions & explanations for ACT Math

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Example Questions

Example Question #101 : Exponents

What is the value of ?  Round to the nearest hundredth.

Possible Answers:

Correct answer:

Explanation:

You could solve this by using your calculator. Remember that you will have to translate this into:

Another way you can solve it is by noticing that 

This means you can rewrite your logarithm:

Applying logarithm rules, you can factor out the power:

For any value . Therefore, . So, your answer is .

Example Question #2291 : Act Math

Solve for 

.

Round to the nearest hundredth.

Possible Answers:

Correct answer:

Explanation:

To solve an exponential equation like this, you need to use logarithms.  This can be translated into:

Now, remember that your calculator needs to have this translated.  The logarithm  is equal to the following:

, which equals approximately .

Remember that you have the equation:

Thus, .

Example Question #2292 : Act Math

Solve the following equation

.

Possible Answers:

Correct answer:

Explanation:

In order to solve a question like this, you will need to use logarithms. First, start by converting this into a basic logarithm:

Recall that you need to convert  for your calculator:

, which equals approximately 

Thus, you can solve for :

Example Question #2293 : Act Math

At the end of each year, an account compounds interest at a rate of .  If the account began with , how many years will it take for it to reach a value of , presuming no withdrawals or deposits occur?

Possible Answers:

Correct answer:

Explanation:

The general function that defines this compounding interest is:

, where  is the number of years.

What we are looking for is:

You can solve this using a logarithm.  First, isolate the variable term by dividing both sides:

Which is:

Next, recall that this is the logarithm:

For this, you will need to do a base conversion:

This is 

This means that it will take  years.   is too few and at the end of , you will have over .

Example Question #2294 : Act Math

What is the value of ?  Round to the nearest hundredth.

Possible Answers:

Correct answer:

Explanation:

Remember that you will need to calculate your logarithm by doing a base conversion. This is done by changing  into:

Using your calculator, you can find this to be:

 or approximately 

Example Question #11 : How To Find A Logarithm

if , what is ?

Possible Answers:

Correct answer:

Explanation:

The first step of this problem is to find

 by expanding to the formula

  

y is found to be 2.  The next step is to plug y in to the second log.  

, which expands to

Example Question #101 : Exponents

Find  .

Possible Answers:

Correct answer:

Explanation:

 

expands to

 

expands to

Example Question #11 : Logarithms

Simplify:

 

Possible Answers:

Correct answer:

Explanation:

Here, we need to make use of some logarithm identities:    

Therefore, putting all of those things together, we get the final answer of 

Example Question #11 : Logarithms

If

,

then what is ?

Possible Answers:

Correct answer:

Explanation:

This is a test of translating logarithmic/exponential properties, with the key here being to realize that

is equivalent to .

With that in mind, here is how it works out:

Hence, .

Example Question #12 : Logarithms

can be written as which of the following?

A.

B.

C.

Possible Answers:

B and C only

A only

B only

A, B and C

A and B only

Correct answer:

A, B and C

Explanation:

A is true in two ways. You can use the fact that if a logarithm has no base, you can use base 10, or you can use the fact that you can use this property:

B is a simple change of base application, and C is simply computing the logarithm.

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