# Illustrative Mathematics Unit 6.6, Lesson 6: Write Expressions Where Letters Stand for Numbers

Learning Targets:

• I can use an expression that represents a situation to find an amount in a story.
• I can write an expression with a variable to represent a calculation where I do not know one of the numbers.

Related Pages
Illustrative Math

#### Lesson 6: Write Expressions Where Letters Stand for Numbers

Let’s use expressions with variables to describe situations.

Illustrative Math Unit 6.6, Lesson 6 (printable worksheets)

#### Lesson 6 Summary

The following diagram shows how to use expressions with variables to describe situations. #### Lesson 6.1 Algebra Talk: When x is 6

Solve each equation. Be prepared to explain your reasoning. If x is 6, what is:

• x + 4
• 7 - x
• x2
• 1/3 x

Scroll down the page for the solutions to the “Are you ready for more?” section.

#### Lesson 6.2 Lemonade Sales and Heights

1. Lin set up a lemonade stand. She sells the lemonade for \$0.50 per cup. a. Complete the table to show how much money she would collect if she sold each number of cups.

 lemonade sold (number of cups) 12 183 c money collected (dollars)

b. How many cups did she sell if she collected \$127.50? Be prepared to explain your reasoning. 2. Elena is 59 inches tall. Some other people are taller than Elena. a. Complete the table to show the height of each person.
 person Andre Lin Noah how much taller than Elena (inches) 4 6 1/2 d person's height (inches)

b. If Noah is 64 3/4 inches tall, how much taller is he than Elena?

#### Lesson 6.3 Building Expressions

1. Clare is 5 years older than her cousin.
a. How old would Clare be if her cousin is:
10 years old?
2 years old?
x years old?
b. Clare is 12 years old. How old is Clare’s cousin?
2. Diego has 3 times as many comic books as Han.
a. How many comic books does Diego have if Han has:
6 comic books?
n books?
b. Diego has 27 comic books. How many comic books does Han have?
3. Two fifths of the vegetables in Priya’s garden are tomatoes.
a. How many tomatoes are there if Priya’s garden has:
20 vegetables?
x vegetables?
b. Priya’s garden has 6 tomatoes. How many total vegetables are there?
4. A school paid \$31.25 for each calculator.
a. If the school bought x calculators, how much did they pay?
b. The school spent \$500 on calculators. How many did the school buy?

#### Are you ready for more?

Kiran, Mai, Jada, and Tyler went to their school carnival. They all won chips that they could exchange for prizes. Kiran won 2/3 as many chips as Jada. Mai won 4 times as many chips as Kiran. Tyler won half as many chips as Mai.

1. Write an expression for the number of chips Tyler won. You should only use one variable: , which stands for the number of chips Jada won.
2. If Jada won 42 chips, how many chips did Tyler, Kiran, and Mai each win?

Number of chips Jada won: J
Number of chips Kiran won: 2/3 J
Number of chips Mai won: 4 · 2/3 J = 8/3 J

1. Number of chips Tyler won: 1/2 · 8/3 J = 4/3 J
2. J = 42
Number of chips Kiran won: 2/3 · 42 = 28
Number of chips Mai won: 8/3 J = 8/3 · 42 = 112
Number of chips Tyler won: 4/3 J = 4/3 · 42 = 56

#### Lesson 6 Practice Problems

1. Instructions for a craft project say that the length of a piece of red ribbon should be 7 inches less than the length of a piece of blue ribbon.
a. How long is the red ribbon if the length of the blue ribbon is:
10 inches?
27 inches?
x inches?
b. How long is the blue ribbon if the red ribbon is 12 inches?
2. Tyler has 3 times as many books as Mai.
a. How many books does Mai have if Tyler has:
15 books?
21 books?
x books?
b. Tyler has 18 books. How many books does Mai have?
3. A bottle holds 24 ounces of water. It has x ounces of water in it.
a. What does 24 - x represent in this situation?
4. Write an equation represented by this tape diagram that uses each of the following operations.
b. subtraction
c. multiplication
d. division
5. Select all the equations that describe each situation and then find the solution.
a. Han’s house is 450 meters from school. Lin’s house is 135 meters closer to school. How far is Lin’s house from school?
z = 450 + 135
z = 450 - 135
z - 135 = 450
z + 135 = 450
b. Tyler’s playlist has 36 songs. Noah’s playlist has one quarter as many songs as Tyler’s playlist. How many songs are on Noah’s playlist?
w = 4 · 36
w = 36 ÷ 4
4w = 36
w/4 = 36
6. You had \$50. You spent 10% of the money on clothes, 20% on games, and the rest on books. How much money was spent on books?
7. A trash bin has a capacity of 50 gallons. What percentage of its capacity is each of the following? Show your reasoning.
a. 5 gallons
b. 30 gallons
c. 45 gallons
d. 100 gallons

The Open Up Resources math curriculum is free to download from the Open Up Resources website and is also available from Illustrative Mathematics.

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