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Defining Variables  Concept
FREEAlissa Fong
Alissa Fong
MA, Stanford University
Teaching in the San Francisco Bay Area
Alissa is currently a teacher in the San Francisco Bay Area and Brightstorm users love her clear, concise explanations of tough concepts
Variables are used throughout math after Algebra, and are important to understand. A defining variable is a symbol, such as x, used to describe any number. When a variable is used in an function, we know that it is not just one constant number, but that it can represent many numbers. Variables are instrumental in understanding problems relating to graphing.
One thing you're going to learn really quickly about algebra is that it's not just involving numbers, but it uses a lot of letters too. And what the letters are, are officially called variables.
A variable is a letter or a symbol used to represent any number. And it's kind of tricky because the letter is going to represent the same number within that specific problem but the same letter could represent different numbers between different problems. Let me show you what I mean.
Let's say I had this problem that said x+5=8. That was like problem one on my homework. And then problem two on my homework said x take away 4 is equal to 10. So you can probably do these in your head, think about what number x might stand for. What number plus gives you the answer 8? Most of you guys in your head can tell x=3. That's problem one.
Look at problem 2. It uses the same letter but it's going to be a different number. What number take away 4 gives us the answer 10? 14. So the trick with variables is that it's the same letter and it represents any number like it could be, sometimes x would be like a fraction, sometimes x will be a decimal but the trick is that it might be different numbers from one problem to the next.
When you come across variables, it's something that's kind of new because you're going to be dealing with letters and numbers. But use your logic and slow down. Think about what the variable stands for and if it helps you, turn it into words in your head like I did. Like what number plus 5 gives you 8. That's a really great strategy to help when you're working with variables.
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Alissa Fong
M.A. in Secondary Mathematics, Stanford University
B.S., Stanford University
Alissa has a quirky sense of humor and a relatable personality that make it easy for students to pay attention and understand the material. She has all the math tips and tricks students are looking for.
Your tutorials are good and you have a personality as well. I hope you have more advanced college level stuff, because I like the way you teach.”
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Sample Problems (4)
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Defining Variables
Problem 1 12,417 viewsWrite the following equation in words:
m⁄4 = 5 
Defining Variables
Problem 2 9,085 viewsEvaluate f − 4 when
a) f = 3b) f = 2 
Defining Variables
Problem 3 8,254 viewsWrite the following using mathematical symbols:
The product of some number and 5 is 80. 
Defining Variables
Problem 4 349 views
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