1. MJ2A
Ch 6.7 – Percent Equation

2. Bellwork Use the percent proportion to find the missing term
128 is what percent of 640?
12 is 80% of what number?
What is 20% of 35?

3. Assignment Review
Text p. 291 #7 – 22

4. Before we begin… Please take out your notebook and get ready to work…
In today’s lesson we will extend what we learned about the percent proportion by looking at a variation of the percent proportion called the percent equation

5. Objective 6.7
Students will solve percent problems using the percent equation.

6. Percent Equation
The percent equation is a variation of the percent proportion. The big difference is that the percent is expressed as a decimal…
The percent equation
Part = Percent ∙ Base
Lets see what this looks like…

7. Example 1 Find 52% of 85 First convert 52% to a decimal (0.52)
You know that 85 is the base
You need to find the part (n)
Then write the formula, substitute and do the math.
Part = Percent ∙ Base
n = 0.52(85)
n = 44.2
Therefore, 52% of 85 is 44.2

8. Example 2 28 is what percent of 70?
You know that the base is 70 and the part is 28. Let p = percent
Write the formula, substitute, and do the math
Part = Percent ∙ Base
28 = p(70)
0.4 = p
Convert the decimal to a percent 0.4 = 40% Therefore, 28 is 40% of 70

9. Example 3 18 is 45% of what number?
You know that the part is 18 and the percent is 45% (0.45). Let b represent the base
Write the formula, substitute, & do the math
Part = Percent ∙ Base
18 = 0.45(b)
40 = b
Therefore, 18 is 45% of 40

10. Your Turn
In the notes section of your notebook write the sentence and then find the missing part using the percent equation.
15 is what percent of 60?
What is 20% of 110?
30 is 60% of what number?

11. Discount You can use the percent equation to calculate discount.
Discount is the amount by which a regular price is reduced
Be careful here…sometimes the question will ask for the discount amount (Which is the original amount times the percent of discount)
Some times it will ask you for the sale price (which is the original price less discount)
Let’s look at an example

12. Example
Mateo wants to buy a skateboard. The regular price of the skateboard is $135. The skateboard is on sale at a 25% discount. What is the sale price?
In this instance they are looking for the sale price…this means you have to calculate discount first and then subtract it from the original price to get the sale price!
We can use the percent equation here to find 25% (0.25)of 135
Part = Percent ∙ Base
d = 0.25(135)
d =
The discount amount is $ Therefore, the sale price is $ ($ – $33.75 = $101.25)

13. Your Turn
In the notes section of your notebook calculate the discount and sale price of the following:
1. The regular price of a ring is $495. It is on sale for 20% discount. What is the sale price of the ring?

14. Simple Interest
Interest is the amount of money paid or earned for the use of money…
To calculate simple interest use the following formula
I = prt
Where I = interest
p = principal
r = rate
t = time

15. Simple Interest
Since we use a formula for simple interest you are to use the formula method when calculating simple interest
The formula method is
Write the formula
Substitute
Do the math.

16. Example
Sandra invests $500 at 5.5% interest. In 2 years how much will she earn?
In this instance $500 represents the principal, represents the rate, and time is 2 years.
I = prt
I = 500(0.055)(2)
I = 500(0.11)
I = 55
Sandra will earn $55.00 interest for investing her money

17. Comments
When working with the simple interest formula you need to know that time is expressed in years.
That means if you have less than a year or time not equal to even amounts of years you need to convert the time into years.
Example:
3 months would be 3/12 of a year or .25 of a year
20 months would be 20/12 of a year or 1.7 of a year

18. Your Turn
In the notes section of your notebook use the simple interest formula to calculate the interest.
1. Ricardo borrows $250 at 9% interest for six months. How much interest will he pay?

19. 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 it?
Discount
Simple Interest

20. Assignment Text p. 301 # 20 – 40 Reminder:
This assignment is due tomorrow
I do not accept late assignments
You do not have to write the sentences. However, you must show how you got your answer (no work = no credit)