This question could be set up like an equation as follows:

The variable  indicates the number of books that would have to be sold.  This comes out to:

Now, don't be tricked!  You can't sell partial books.  Thus, you will need to sell  books in order to turn a profit.  If you only sell , you will not have sold enough to make a profit.

This question is a bit hard.  You need to think it out step by step.  First, you could write an equation like this:

This represents the idea of trying to calculate when the profit per book will be three dollars.  Now, we know that profit is equal to:

Thus, you can rewrite your equation:

Now, the original cost is calculated by multiplying  by .  This is the same as .  The sales amount is just , where  indicates the total number of books sold.  This will also be the total for  in your equation.  Thus, you can write out the following equation:

Now, just solve for :

However, you will need to sell one more book than .  (That would be just a little too insufficient.)  Thus, the answer is .

Timmy makes ten dollars per hour for eight hours.

For five days:  

Timmy also will pay  for the week to get to work and back.

Subtract his expense from his earnings for the week.

Timmy will have  by the end of the week.

Recall the formula for calculating the interest:

, where  is the amount of interest generated,  is the principle (initial deposit),  is the interest rate, and  is the time in years.

Since the question asks for a length of time, we will need to solve for .

Plug in the given information and solve for .

Recall that  is given in years. However, the question wants the number of months the money was deposited for. Thus, multiply by  to get the number of months.

The money was deposited for  months.

Calculate how much Richard will earn per day.

For five hours at an hourly wage of :  

He will work five days per week.  At the end of 2 week period, Richard will have worked a total of 10 days.

Multiply the  per day with 10 to get the total amount.

The answer is:  

Because the question states that Joseph can spend up to , we know that we will be using a less than or equal to sign. We cannot use an equal sign because that means Joseph will be spending exactly .

Since each video game costs , that means if Joseph buys  number of games, he will spend .

Thus, the conditions of his purchase can be illustrated by .

Let  be the original cost of the computer.

Since we have taken  off,  can represent the amount that is taken off.

We can then write the following equation:

Now solve for .

First, calculate the cost for the miles driven. Since the rider will be charged  for every mile driven, we can write the expression  to illustrate the total mileage cost.

Next, since the problem states that  will be a one-time charge on the fare, we can then write the following expression to illustrate the total cost of a taxi ride of  miles: 

Let  be the number of quarters. Then there are  dimes.

An equation can be set up and solved for  for the amount of money in dollars:

Translate the words into a mathematical equation. "Three times a number squared" can be written as . "Less " is telling you to subtract  from .

We can then write the following equation, then solve for .