© teacher created materials today’s lesson writing algebraic expressions

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Today’s Lesson

Writing Algebraic

Expressions

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Let’s warm up today by finding patterns in numbers.

Warm-Up Activity

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Find the missing numbers in the following patterns.

3, 6, 9, __ , 15, 18, __ , 24

1, 2, 4, __ , 11, 16, __ , 29

1, 1, 2, 3, 5, __ , 13, __

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Check your answers.

3, 6, 9, 12, 15, 18, 21, 24

1, 2, 4, 7, 11, 16, 22, 29

1, 1, 2, 3, 5, 8, 13, 21

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What is the pattern?

3, 6, 9, 12, 15, 18, 21, 24

+3 each time

+3 +3 +3 …

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What is the pattern?

+1 more each time

+1 +2 +3 +4 …

1, 2, 4, 7, 11, 16, 22, 29

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What is the pattern?

Add the 2 previousnumbers together

+0 +1 +1 +2 +3 +5 +8 1, 1, 2, 3, 5, 8, 13, 21

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Today we will write algebraic expressions and find patterns in real-life situations to show

algebraically.

Whole-Class Skills Lesson

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To review, what does the word variable mean?

A variable is an unknown quantity that has the potential to change.

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What does the term algebraic expression mean?

An algebraic expression is any number sentence using variable(s) and number(s) in any combination.

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How would you write the following expressions?

A number that is 5 more than 8

A number that is 5 more than t

A number that is 3 less than f

A number that is t less than f

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How would you write the following expressions?

A number that is 5 more than 8

A number that is 5 more than t

A number that is 3 less than f

A number that is t less than f

8 + 5

t + 5

f – 3

f – t

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Judy and her sister are born in the same month, but in different years. Judy is 5 years old and her sister is 2. When Judy turns 8, her sister will be 5. How old will Judy’s sister be when Judy is 14?

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How did you solve that problem?

Just one of the ways to solve this problem is to make a T-chart.

This is a T-chart.

Judy’s age Sister’s age

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Copy the T-chart below

Copy the data for Judy and her sister’s ages. This data comes

from the problem.

Judy’s age Sister’s age

5 2

8 5

14

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Do you see a pattern with Judy and her sister’s ages?

Judy’s age Sister’s age

5 2

8 5

14

Judy’s sister’s age is always 3 years less than Judy’s age.

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So based on the pattern, when Judy is 14, her sister will be three

years less than that—11 years old.

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How old will Judy’s sister be when Judy is 20?

20 – 3 = 17

Judy’s sister will be 17.

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How old will Judy’s sister be when Judy is 25?

25 – 3 = 22

Judy’s sister will be 22.

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Assign a variable to Judy’s age.

Judy’s age Sister’s age

5 2

8 5

14

Judy’s age can be represented by a variable, j

j

11

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What is the best way to figure out Judy’s sister’s age using j as a

starting point?

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We can write an algebraic for Judy’s sister’s age.

j – 3

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Using j – 3, solve for Judy’s sister’s age when

j = 31

31 – 3 = 28

j = 45

45 – 3 = 42