Writing Algebraic Expressions

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Writing Algebraic Expressions

• Lesson 2-3

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Word phrases can be written as algebraic
expressions.

• Use the words to determine what operation you are
  using.
• Use a variable for the phrase a number.

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Adding Phrases

• Plus
• More than
• Sum
• Increased by

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Subtracting Phrases

• Minus
• Difference
• Subtracted from
• Decreased by
• Less than

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Multiplying Phrases

• Times
• Product of

Dividing Phrases

• Quotient
• Divided by

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Example 7 decreased by b
Decreased by means subtract.
7 - b
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Example The product of 19 and k
Product means multiply. We show multiplication
by placing the factor right next to the variable.
19k
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Less than, more than

• Some word phrases contain the words less than
  or more than.
• When you see those words, start with the second
  part of the phrase.

Example 23 less than m
m - 23
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Example 32 less than 5 times c
The 32 is less than the 5 times c, which means we
subtract 32 from the 5 times c. So, start with 5
times c.
5c - 32
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Tables

• When you are given a table of values, determine
  how to get from the first column to the second
  column.
• Describe that pattern with an algebraic
  expression.

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Example
n
?
3
12
7
28
11
44
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Compare from left to right.

• How do we get from 3 to 12? Add 9 or multiply by
  4.
• How do we get from 7 to 28? Multiply by 4.
• If we multiply 11 by 4, we get 44.

The pattern is to multiply our number, n, by 4.
The algebraic expression to describe this is 4n
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Describing Unknown Numbers

• When you dont know what a number is, let a
  variable stand for that number.
• Use an algebraic expression to describe what
  youre looking for.

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Example
Write an algebraic expression to describe Jerrys
age. Use the following information Jerry is 4
years younger than his brother Steve.
First, we have to know how old Steve is. We do
not have an age for Steve, so we will use a
variable Let s Steves age.
Now that we have determined Steves age (s), we
can use it to determine Jerrys age. Jerry is 4
years younger than Steve.
s - 4
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If Steve is 22 years old, then how old is Jerry?
s - 4
Jerry is 18 years old.
22 - 4
18
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Homework Time