Algebra Help - How Do I Write An Equation?

By Stuart Ackerman  MSc.Ed.,B.A.

     In algebra, an equation is considered a ‘number sentence’.   An equation is a math expression that has an equals sign. 

     So, we can say that an equation is a mathematical sentence that contains an equals sign.  An equation tells us that two expressions have the same meaning.  That is, the two expressions represent the same number.  Algebraic equations contain variables and constant numbers.  We can use equations to solve math problems.

     Here are some examples of equations:

E.g. #1

4m + 3 = 15       x - 5 = 21       y + 2y = 3

When using algebra, it is important to translate a word problem into the correct equation so that you can efficiently solve the problem.

E.g. #2

A number y times 4 is equal to 24.

The word "times" tells you that you have to multiply the variable y by 4, and that the result is equal to 24.  We would write the equation like this:

4y = 24

E.g. #3

Ten dollars was one quarter of the total money spent.

What are we trying to figure out? The unknown amount is the total money spent. Let's call this x. We know that ten dollars is equal to, so we can write the equation like this:

¼x = $10

Here are some important ideas to consider when solving algebraic expressions:

1.  What was that variable?
2.  It's a good idea to write down what your variables mean.

     For example, write this equation:   

     Today, a girl is twice as old as her  brother.    

     So, we can say:  Let x represent the gir's age.

3.  Units.  Remember to include units (e.g. $, km, feet, %). If you have a real-world problem that uses units, keeping the units in the equation will help you figure it out.

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