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 night tickets (evening shows).
Let d be the number of day 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.
|English Words||Translation into Math||Notes/Conventions|
|"Antonio went to see a total ofmovies"||There are many real-number choices for n and d that make this equation true.
Here are a few:
Of course, we want whole number solutions, and we also need something else to be true.
|"... and spent"||
Each night movie costs, so n night movies cost dollars.
Each day movie costs, so d day movies cost dollars.
Both 8n and 6d have units of dollars.
Convince yourself that there are also infinitely many real-number choices for n and d that make this equation true.
We want a choice for n, and a choice for d, that make BOTH equations true at the same time.
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 equationis simpler than .
We could solve the equationfor either or ;
hmmm…… think I will choose to solve for. (It does not matter!)
Subtracting dd from both sides, we get:
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.
Substitutinginto the equation gives:
Solve the resulting equation in one variable. Be sure to write a nice, clean list of equivalent equations.
|combine like terms|
|subtractfrom both sides|
|divide both sides by|
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 bothand are true, then d must equal 5.
|the simple equation|
|substitute in the known information|
|subtract 55 from both sides|
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|
The original problem asked how many night movies Antonio attended, so here is what you would report as your answer:
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:
|Antonio loves to go to the movies. He goes both at night and during the day. The cost of a matinee is. The cost of an evening show is . If Antonio went to see a total of 12 movies and spent , how many night movies did he attend?|
Let n=# night tickets.
Let d=# day tickets.
Source: Tree of Math, https://www.onemathematicalcat.org/algebra_book/online_problems/simple_word_probs.htm
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