Read this article for another example of this type of a general statement problem. In this problem, it looks like there are two variables. However, we can relate the quantity of one variable to that of the other. This allows us to write the equation in terms of only one variable.

At the bottom of the page, try a few practice problems and check your answers. Try a couple of these until you feel comfortable writing and solving equations from general word problems.

Many word problems, upon translation, result in two equations involving two variables (two "unknowns"). In mathematics, a collection of more than one equation being studied together is called a **system of equations**.

The systems in this section are fairly simple, and can be solved by substituting information from one equation into the other. The procedure is illustrated in the following example:

Decide what piece(s) of information are **unknown**, and give name(s) to these things.

Choose names that help you to remember what they represent!

Let n be the number of **n**ight tickets (evening shows).

Let d be the number of **d**ay tickets (matinee shows).

Re-read the word problem.

The English words will translate into mathematical sentences involving your unknowns.

You may need additional mathematical concepts in making your translation.

STEP 3: Choose a Simplest Equation, and Solve for One Variable in Terms of the Other

Remember that to **solve for a variable** means to get it all by itself, on one side of the equation, with none of that variable on the other side.

Here, you are getting a **new name** for one of your variables that is helpful for finding the solution.

Clearly, the equation is simpler than .

We could solve the equation for either or ;

hmmm…… think I will choose to solve for . (It does not matter!)

Subtracting dd from both sides, we get:

STEP 4: Use Your New Name in the Other Equation

Take your new name from the previous step, and substitute it into the remaining equation.

This will give you an equation that has only one unknown.

Substituting into the equation gives:

STEP 5: Solve the Equation for One Unknown

Solve the resulting equation in one variable. Be sure to write a nice, clean list of equivalent equations.

original equation | |

distributive law | |

combine like terms | |

subtract from both sides | |

divide both sides by |

STEP 6: Use the Known Variable to Find the Remaining Variable

Go back to the simplest equation, substitute in your new information, and solve for the remaining variable.

Make sure you understand the logic being used:

If both and are true, then d must equal 5.

Substitute into the simple equation and solve:

the simple equation | |

substitute in the known information | |

subtract 55 from both sides |

STEP 7: Check and Report Your Answers

Check that the numbers you have found make both of the equations true.

Then, report your answer(s) using a complete English sentence.

Equations | Check | Is it True |

Does | Yes! | |

Does | Yes! |

The original problem asked how many night movies Antonio attended, so here is what you would report as your answer:

The Good News!

Even though this explanation was **very long**, you will actually be writing down **very little**!

Here is the word problem again, and what I ask my students to write down:

Source: Tree of Math, https://www.onemathematicalcat.org/algebra_book/online_problems/simple_word_probs.htm

This work is licensed under a Creative Commons Attribution-NonCommercial 2.5 License.

Last modified: Wednesday, May 5, 2021, 2:23 PM