Jeremy read that degrees Celsius converted to degrees Fahrenheit is "the sum of 32 and \begin{align*}\frac{9}{5}\end{align*}

### Writing Algebraic Expressions

In mathematics, especially in algebra, we look for patterns in the numbers that we see. Using mathematical verbs and variables, expressions can be written to describe a pattern. Recall that an **algebraic expression** is a mathematical phrase combining numbers and/or variables using mathematical operations. We can describe patterns using phrases as well, and we want to be able to translate these phrases into algebraic expressions.

Consider a theme park charging an admission of $28 per person. A rule can be written to describe the relationship between the amount of money taken at the ticket booth and the number of people entering the park. In words, the relationship can be stated as “The money taken in dollars is (equals) twenty-eight times the number of people who enter the park.”

The English phrase above can be translated (written in another language) into an algebraic expression. Using mathematical verbs and nouns, any phrase can be written as an algebraic expression.

#### Let's write an algebraic expression for the each of the following phrases:

- The product of \begin{align*}c\end{align*}
c and 4.

The verb is product, meaning “to multiply.” Therefore, the phrase is asking for the answer found by multiplying \begin{align*}c\end{align*}

- The phrase about the theme park from above: The money taken in dollars is (equals) twenty-eight times the number of people who enter the park.

An appropriate variable to describe the number of people could be \begin{align*}p\end{align*}

- 5 less than 2 times a number.

Some phrases are harder to translate than others. The word "less" lets you know that you are going to take away, or subtract, a number. Many students will want to turn this expression into \begin{align*}5-2n\end{align*}

### Examples

#### Example 1

Earlier, you were asked told that the degrees Fahrenheit temperature is "the sum of 32 and \begin{align*}\frac{9}{5}\end{align*}

We can use \begin{align*}c\end{align*}

\begin{align*}32 + \frac{9}{5}c\end{align*}

#### Example 2

A student organization sells shirts to raise money for events and activities. The shirts are printed with the organization's logo and the total costs are $100 plus $7 for each shirt. The students sell the shirts for $15 each. Write an expression for the cost and an expression for the revenue (money earned).

We can use \begin{align*}x\end{align*}

### Review

For exercises 1 – 15, translate the English phrase into an algebraic expression. For the exercises without a stated variable, choose a letter to represent the unknown quantity.

- Sixteen more than a number
- The quotient of \begin{align*}h\end{align*}
h and 8 - Forty-two less than \begin{align*}y\end{align*}
y - The product of \begin{align*}k\end{align*}
k and three - The sum of \begin{align*}g\end{align*}
g and \begin{align*}-7\end{align*}−7 - \begin{align*}r\end{align*}
r minus 5.8 - 6 more than 5 times a number
- 6 divided by a number minus 12
- A number divided by \begin{align*}-11\end{align*}
−11 - 27 less than a number times four
- The quotient of 9.6 and \begin{align*}m\end{align*}
m - 2 less than 10 times a number
- The quotient of \begin{align*}d\end{align*}
d and five times \begin{align*}s\end{align*}s - 35 less than \begin{align*}x\end{align*}
x - The product of 6, \begin{align*}-9\end{align*}
−9 , and \begin{align*}u\end{align*}u

In exercises 16 – 24, write an English phrase for each algebraic expression

- \begin{align*}J - 9\end{align*}
J−9 - \begin{align*}\frac{n}{14}\end{align*}
n14 - \begin{align*}17-a\end{align*}
17−a - \begin{align*}3l-16\end{align*}
3l−16 - \begin{align*}\frac{1}{2} (h)(b)\end{align*}
12(h)(b) - \begin{align*}\frac{b}{3} + \frac{z}{2}\end{align*}
b3+z2 - \begin{align*}4.7-2f\end{align*}
4.7−2f - \begin{align*}5.8 + k\end{align*}
5.8+k - \begin{align*}2l+2w\end{align*}
2l+2w

In exercises 25 – 28, define a variable to represent the unknown quantity and write an expression to describe the situation.

- The unit cost represents the quotient of the total cost and number of items purchased. Write an expression to represent the unit cost of the following: The total cost is $14.50 for \begin{align*}n\end{align*}
n objects. - The area of a square is the side length squared.
- The total length of ribbon needed to make dance outfits is 15 times the number of outfits.
- What is the remaining amount of chocolate squares if you started with 16 and have eaten some?

Use your sense of variables and operations to answer the following questions.

- Describe a real-world situation that can be represented by \begin{align*}h + 9\end{align*}
h+9 . - What is the difference between \begin{align*}\frac{7}{m}\end{align*}
7m and \begin{align*}\frac{m}{7}\end{align*}m7 ?

### Review (Answers)

To see the Review answers, open this PDF file and look for section 1.6.