Finding a percent of a number
Textbook pages 434-440
January 14th, 15th, 16th
Objective
• I can find the percent of a quantity.
• I can solve problems involving finding the
whole, if given the part of the whole and
percent
Review Vocabulary
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Is means
Equal =
Of means to
multiply.
Equations are going to be very important in
this lesson.
• Reminder, in order to solve equations you
have to do the opposite.
New Vocabulary
• Interest: is the amount paid to use money.
• Principal; the amount of money you borrow or
save.
• Annual interest rate: the amount of money
you earn or pay per year
Finding the percent of a Number
• There are three ways to find the percent of a
number.
• Change the percent to a decimal then multiply.
• Change the percent to a fraction then multiply.
• By making a proportion.
• Lets see what you find easier.
• 50% of 8
• What way did you use?
Try some more!
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Find 25% of 48
12, explain how you found your answer
10% of 85
8.5
45% 0f 20
9
60% of 60
36
Find the whole number given the part
and percent
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25% of what number is 8
Rewrite as an equation.
.25 x n = 8
How do I solve?
Divide both sides by .25
The answer is 32
Try some!
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20% of what number is 30
150
40% of what number is 60
150
75% of what number is 54
72
Finding a discount
• What is a discount? Give me an example
• The discount is the amount that you will get off
of the regular price.
• Find the discount, (by finding the percent of the
number) usually a percent off.
• Then subtract from the original price, the answer
you get is the sale price.
Example
• A pair of pants cost $36. The sale price is 25%
off the regular price. What is the sale price?
• 25% of $36
• What are we going to change 25% to.
• 0.25 x $36
• $9
• Then subtract from the original price.
• $36-$9
• $27 is he sale price of the pants
Try some
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A regular price for a shirt is $40.
Find the sale price if the discount is 15%.
$34
Find the sale price if the discount is 40%
$24
Is there another way!
• Can anyone think of another way to do these
types of problem.
• If you know that you will not have to pay the
discount part, you will pay whatever percent is
left.
• If there is a 30% discount, that means you will
pay 70% of the amount. This eliminates one
step.
Finding Sales Tax
• Sales Tax is something extra you have to pay
besides the price of something.
• Anyone know what the sales tax is in Lorain
county?
• Find the sales tax the same way you find the
percent of a number, then add that to the
original number.
Example
• You are buying cat food for $9. The sales tax is
6%. What is the total of the purchase?
• 6% x 9
• 0.06 x 9
• .54 cents
• $9.00 + .54 = $9.54
Try One!
• Cat toy is $8.00. The sales Tax is 6%. What is
the cost.
• $8.48
• You are buying a pair of shoes that cost
$28.80. There is a 5% sales tax. What is the
total amount of your purchase.
• $30.24
Tips
• A tip is added to the total of a bill. It is found
the same way that you find the percent of a
number.
• Standard tipping amount is what?
Simple Interest
• Interest paid on only the principal.
• Formula
• SI=Principal x annual interest Rate x Time in years
Percent of change
• This can be either percent increase or percent
decrease.
• P%=amount of increase/original amount
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P%=amount of decrease/original amount
What is the percent change from 8 to 13?
62.5%
What is the percent change from 60 to 12?
80%
Try some.
• A taco company puts 24 taco shells in every
box. Recently the company expanded the box
and put 25% more shells in each box. How
many more shells are in each box?
• 25% of 24
• .25 x 24 = 6
• 24 + 6 = 30 shells
Finding the mark-up
• A store that sells skateboards buys them from
a manufacturer at a wholesale price of $57.
The store’s mark-up is 150%. What is the retail
price?