MJ2
Ch 8.2 – The Percent Equation
1. Figure EFGH and ADCD are similar. The ratio of their
corresponding sides is 1:2. What is the length of EF ?
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1 n
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2 7
C
A
7cm
2n = 7
1
n  3 cm
2
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Bellwork – You do not have to write the
question
Before we begin…
• Please take out your notebook and get
ready to work….
• In today’s lesson we will continue with
the chapter theme of applying
percents…more specifically, in today’s
lesson we will look at the percent
equation, which is a formula…
Objective
• Students will solve problems using the
percent equation.
The Percent Equation
• The percent equation is a variation of
the percent proportion…the big
difference is that in the percent equation
the percent is expressed as a decimal.
• The percent equation uses the following
formula
part = percent ● base
Using Formula’s
•
Whenever you work with a formula you are to
use the following strategy…
1. Write the formula
2. Substitute
3. Do the math
•
•
You must show each step…and rewrite the
equation after each operation
At this level you are required to demonstrate
what you know….this is how you do that!
Example
• What number is 12% of 350?
• Before I begin…I have to know some
stuff…like…
• 12% expressed as a decimal is 0.12
• 350 is the base
• I need to find the part, which I will call n..
• Now…lets work it out using the formula
method…
Example…
part = percent ● base
n = 0.12 ● 350
n = 42
• Therefore, 42 is 12%
of 350
1. Write the formula
2. Substitute
3. Do the math
How to identify the parts of the
percent equation
• Most often these types of problems are word problems…
• Key phrases tell use what they are looking for as follows:
To find the part you might have a question like this
What number is 50% of 6?
To find the percent you might have a question like this
3 is what percent of 6?
To find the base you might have a question like this
3 is 50% of what number?
Your Turn
•
In the notes section of your notebook
write the expression and then use the
percent equation to solve
1. 21 is what percent of 40?
2. 12 is 26% of what number?
3. What number is 88% of 300?
Summary
• In the notes section of your notebook
summarize the key concepts covered in
today’s lesson
• Today we discussed:
• The percent equation
• What is the formula?
• How can you tell what the part, base and
percent are?
Assignment
• Text p. 342 # 8 – 24
Reminder
• This assignment is due tomorrow
• I do not accept late assignments
• You do not have to write the question.
However, you must use the formula method,
step by step, to solve each problem.
• You must show your work (no work = no credit)