Lesson 4.1: Write and Evaluate Algebraic Expressions

​Lesson 4.1

Write and Evaluate Algebraic Expressions​

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​Definition:

Variable: A placeholder for a number we do not know yet. A variable can be anything, but we commonly see them written as letters.​

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Expression: An expression is like a math sentence. It is a combination of variables and terms (numbers).​

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Subject | Subject

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​Key Concept:

We can use variables to help us write and solve word problems. We will see this in problems about weight, money and change over time as well as many other topics.​

Subject | Subject

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​The WWW method:

​What do we know?

​What does this mean?

​What can we do with this?

​Example: A tank containing 35 gallons of water is leaking at a rate of 1/4 gallons per minute. Write an expression for this situation.

​Example: A tree that began at 6 feet and increases by 2 feet per year. Let y represent the number of years.

​Example: The expression -120 + 13m represents a submarine that began at a depth of 120 feet below sea level and ascended at a rate of 13 feet per minute. What was the depth of the submarine after 6 minutes?

Multiple Choice

A tank already has 20 gallons of water in it. It is being filled at a rate of 1/2 gallon per minute. What expression models this situation?

• 20m - 1/2

• 20 - 1/2m

• 20 + 1/2m

• 20m + 1/2

Multiple Choice

Write an expression to model a person who began at 4ft and grows 1/4 ft per year.

• 4y + 1/4

• 4y - 1/4

• 4 + (1/4)y

• 4 - (1/4)y

Multiple Choice

The expression -150 + 10m represents a submarine's depth as it is rising to the surface. What is the submarine's position after 10 minutes.

• -100

• -250

• -50

• 50

Multiple Choice

Evaluate the expression 3x + 5 for x = 6

• 14

• 23

• 13

• 18

Multiple Choice

Evaluate the expression for m = 4

0.5m - 8

• 10

• -3.5

• -6

• 6

​Conclusion: Write two complete sentences about what you learned.