© 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