ACT Math : Exponents

Study concepts, example questions & explanations for ACT Math

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Example Questions

Example Question #191 : Exponents

If a cash deposit account is opened with  for a three year period at % interest compounded once annually, which of the following is closest to the positive difference between the interest accrued in the third year and the interest accrued in the second year?

Possible Answers:

Correct answer:

Explanation:

It is easiest to break this down into steps. For each year, you will multiply by  to calculate the new value. Therefore, let's make a chart:

After year 1: ; Total interest: 

After year 2: ; Let us round this to ; Total interest: 

After year 3: ; Let us round this to ; Total interest: 

Thus, the positive difference of the interest from the last period and the interest from the first period is: 

Example Question #2 : How To Find Compound Interest

If an account has interest compounded annually at a rate of , what is the balance of the account after  years of compounding if the initial balance is ? Round to the nearest cent.

Possible Answers:

Correct answer:

Explanation:

Recall that the equation for compounded interest (with annual compounding) is:

Where  is the balance,  is the rate of interest, and  is the number of years.

Thus, for our data, we need to know:

This is approximately .

Example Question #3 : Pattern Behaviors In Exponents

If an account has interest compounded annually at a rate of , what is the balance of the account after  years of compounding if the initial balance is ? Round to the nearest cent.

Possible Answers:

Correct answer:

Explanation:

Recall that the equation for compounded interest (with annual compounding) is:

Where  is the balance,  is the rate of interest, and  is the number of years.

Thus, for our data, we need to know:

This is approximately .

Example Question #3 : How To Find Compound Interest

If an account has interest compounded quarterly at an annual rate of , what is the balance of the account after  years of compounding if the initial balance is ? Round to the nearest cent.

Possible Answers:

Correct answer:

Explanation:

Recall that the equation for compounded interest (with quarterly compounding) is:

Where  is the balance,  is the rate of interest,  is the number of years, and  is the number of times it is compounded per year.

Thus, for our data, we need to know:

This is approximately .

Example Question #4 : How To Find Compound Interest

An account is compounded at a given rate of interest annually for  years.  What is this rate if the beginning balance for the account was  and its ending balance ? Round to the nearest hundredth of a percent.

Possible Answers:

Correct answer:

Explanation:

Recall that the equation for compounded interest (with annual compounding) is:

Where  is the balance,  is the rate of interest, and  is the number of years.

Thus, for our data, we need to know:

Now, let's use  for . This gives us:

Using a logarithm, this can be rewritten:

This can be rewritten:

Now, you can solve for :

or

Now, finally you can rewrite this as:

Thus, 

Now, round this to  and recall that 

Thus,  and  or 

Example Question #192 : Exponents

Jack has , to invest. If he invests two-thirds of it into a high-yield savings account with an annual interest rate of , compounded quarterly, and the other third in a regular savings account at  simple interest, how much does Jack earn after one year?

Possible Answers:

Correct answer:

Explanation:

First, break the problem into two segments: the amount Jack invests in the high-yield savings, and the amount Jack invests in the simple interest account (10,000 and 5,000 respectively).

Now let's work with the high-yield savings account. $10,000 is invested at an annual rate of 8%, compounded quarterly. We can use the compound interest formula to solve:

Plug in the values given:

Therefore, Jack makes $824.32 off his high-yield savings account. Now let's calculate the other interest:

 

Add the two together, and we see that Jack makes a total of,  off of his investments.

Example Question #1 : How To Find Compound Interest

Michelle makes a bank deposit of $1,500 at 4.2% annual interest, compounded monthly. Approximately how much money will be in Michelle’s bank account in 3 years?

 

Possible Answers:

$1,693

$1,701

$1,695

$1,697

Correct answer:

$1,701

Explanation:

The formula to use for compounded interest is  

where P is the principal (original) amount, r is the interest rate (expressed in decimal form), n is the number of times per year the interest compounds, and t is the total number of years the money is left in the bank. In this problem, P=1,500, r=0.042, n=12, and t=3.

By plugging in, we find that Michelle will have about $1,701 at the end of three years.

 

 

Example Question #193 : Exponents

For which of the following values of n will (3)n  represent a real number between 0 and 1?

Possible Answers:

2

2

1

1

0

Correct answer:

2

Explanation:

In order to transform a negative integer to a positive one, it must be taken to an even power, and to make it a fraction between 0 and 1, it must be taken to a negative power. The only choice that fits both criteria is -2. 

Example Question #2 : How To Find Patterns In Exponents

A professional football player’s contract states that he will earn a salary of $1 million his first year.  He would then have a 15% increase every year thereafter for the next 5 years.  What would he make in his 6th and final season on the contract? 

Possible Answers:

Correct answer:

Explanation:

We can represent this as an exponential equation (just use million as a label and not a variable):

$1m * (1.15)5 = $2.01m

Example Question #3 : How To Find Patterns In Exponents

What is the value of the expression , given that  ?

 

Possible Answers:

Correct answer:

Explanation:

First, calculate the value of m by taking the two-thirds root of both m3/2 and 64, leaving m=16. Then solve the expression by plugging in 16 for m. This gives 162 + 3(16) = 256 + 48 = 304.

 

 

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