Main content

### Course: Algebra (all content) > Unit 1

Lesson 5: Writing algebraic expressions introduction- Writing basic expressions with variables
- Writing basic expressions with variables
- Writing basic expressions with variables
- Writing expressions with variables
- Writing expressions with variables
- Writing expressions with variables & parentheses
- Writing expressions

© 2024 Khan AcademyTerms of usePrivacy PolicyCookie Notice

# Writing basic expressions with variables

Learn to write expressions for phrases like "3 more than x."

## Why do we have math if we can describe things in words?

Algebraic expressions are useful because they represent the value of an expression for all of the values a variable can take on.

Sometimes in math, we describe an expression with a phrase. For example, the phrase

"two more than five"

can be written as the expression

Similarly, when we describe an expression in words that includes a variable, we're describing an algebraic expression, an expression with a variable.

For example,

"three more than $x$ "

can be written as the algebraic expression

But why? Why use math if we can describe things in words? One of the many reasons is that math is more precise and easier to work with than words are. This is a question you should keep thinking about as we dig deeper into algebra.

## Different words for addition, subtraction, multiplication, and division

Here is a table that summarizes common words for each operation:

Operation | Words | Example algebraic expression |
---|---|---|

Addition | Plus, sum, more than, increased by | |

Subtraction | Subtracted, minus, difference, less than, decreased by | |

Multiplication | Times, product | |

Division | Divided, quotient |

For example, the word product tells us to use multiplication. So, the phrase

"the product of eight and $k$ "

can be written as

## Let's take a look at a trickier example

**Write an expression for "**$m$ decreased by seven".

Notice that the phrase "decreased by" tells us to use subtraction.

So, the expression is $m-7$ .

## Let's try some practice problems!

## Want to join the conversation?

- why does the square over the square mean divided? Why cant we have an actual division sign?(74 votes)
- That is a common way to represent division in algebra, the division sign is not really used there. Have you noticed that the division sign is a fraction line with two dots representing the numerator and denominator? It evolved from the fraction idea to make it a simpler concept in arithmetic.(76 votes)

- How could algebraic expression be used in everyday life?(48 votes)
- That's a great question! There are lots of different ways algebraic expressions are used in everyday life. For instance: computer programming/computer science. Take a look at the CS tutorials on Khan Academy and you'll see what I mean. Also, Algebra is a useful, logical way to help explain things. Just the other day my mom used math to help teach a group of girls how to make a beaded ring. You can even use algebraic expressions to provide situations, like when giving the rules to a game.

Hopefully this helped, and you'll look into the hundreds of other ways that algebraic expressions are used every day.(71 votes)

- Can their be more than 1 variable like 3xp(24 votes)
- So I’ve got a math question but can’t understand the second part.

Here’s the problem, I’ve got the first half figured out.

If the sum of twice a number and -7 is increased by 8, the result is 16 greater than the opposite of the number. What is the number?

( how do I write 16 greater than?)(7 votes)- Saying that n is the number:

- Come up with a formula.

2n + (-7) + 8 = -n + 16

- 16 greater than the opposite of the number is the same as saying -n (opposite of number) + 16 (16 greater than). Tip: When someone says "greater than" they are typically talking about addition, and when someone says "less than" they are typically talking about subtraction.

- Next, simplify.

2n + 1 = -n + 16

- Subtract 1 and add n to both sides.

2n + n = 16 - 1

- Simplify.

3n = 15

- Divide both sides by 3.

n = 5 <-- answer!

I hope this answer helps you out, and have a great day!(22 votes)

- So we had an expression about division, and it's usually not as sweet and straightforward with obvious words like these. My questions is, what are other ways to say 'divided by' and can you give me examples?(10 votes)
- You can say 'divided by' like this:

/,

The division sign,

and in fraction form.

Unfortunately, you can't really do the division sign or fraction form on a computer, so you have to stick to the /.(10 votes)

- Is't 'of' a multiplication word?(5 votes)
- Yes, "of" is a multiplication word when used with percents and fractions. For example:

20% of a number = 0.2 times x = 0.2x

1/2 of a number = 1/2 times x = (1/2)x(18 votes)

- why is fraction considered as a division?(8 votes)
- I like to think of fractions as segments of a pie or cake. Lets say you & I split (divide) a cake, we take the 1 whole cake & slice it down the middle. On the plate is still 1 whole cake or we could say there are two halves (2/2), if we divide 2 by 2 we get 1 or a whole cake (2/2). You take your half (1/2), now I have one half (1/2). If we divide 1 by 2 (1/2) we get 0.5 or a half! Hope that helps!(11 votes)

- did people used math in the stoneage(3 votes)
- There are archaeological discoveries of bones with tally marks in them, which suggests that stone age humans had some concept of counting and numbers.(17 votes)

- y more than 7(6 votes)
- Hint: The table of key words at the top of the page gives you the meaning of the words "more than". Give it a try.(10 votes)

- let x=10+4+"Dollars"; what is the value of variable x?(3 votes)
- It is impossible to find the value of "x". You basically have an equation with two variables: "x" and "dollars". So, you don't have enough info to find one specific value of "x". Its value will change as the value of "dollars" changes. So, you equation has infinite solutions.(11 votes)