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Percent of a number Lesson 1

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**Find the Percent of a Number**

To find the percent of a number, choose one of the methods 1. Write percent as a fraction and then multiply. OR 2. Write percent as a decimal and then multiply.

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Example 1 Find 5% of 300 by writing the percent as a fraction. 5% = = of 300 = 1 20 x x = = 30 2 = 15 1 = 15 So, 5% of 300 is 15.

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Example 2 Find 25% of 180 by writing the percent as a decimal. 25% = of 180 = 0.25 x 180 Solve this without a calculator. So, 25% of 180 is 45.

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Got it? Find the percent of each number. a. 40% of 70 b. 15% of 100 c. 55% of 160 d. 75% of 280 28 15 88 210

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**Use Percents Greater Than 100%**

150% = = = = 1.5

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Example 3 Find 120% of 75 by writing the percent as a fraction. Write 120% as of of 75 = 6 5 x x 75 1 = 6 1 x x 15 = 90 So, 120% of 75 is 90.

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Example 4 Find 150% of 28 by writing the percent as a decimal. Write 150% as of x 28 = 42 So, 150% of 28 is 45.

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Got it? Find each number. a. 150% of 20 b. 160% of 35 30 56

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**So, about 63 students can be expected to have a 3 TV’s in their house.**

Example 5 Refer to the graph. If 275 students took the survey, how many can be expected to have 3 TV’s in each of their houses? 23% of x 275 = 63.25 So, about 63 students can be expected to have a 3 TV’s in their house.

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**Percent and estimation**

Lesson 2

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**Estimate the Percent of a Number**

Sometimes an exact answer is not needed when using percents. Take 70%. 70% = = % = 7 x 10%

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Example 1 Jodi has paid 62% of the $500 she owes for her loan. Estimate 62% of % of 500 ≈ 60% of % = x 500 = 300 So, 62% of $500 is about $300.

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Example 2 Marita and four of her friends ordered a pizza that cost $ She is responsible for 20% of the bill. About how much money will she need to pay? $14.72 is close to $15. Find 10% of 15, which is $1.5. Multiply $1.5 by 2, since 20% is twice as much as 10%. $1.5 x 2 = $3.00 Marita should pay about $3.00.

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**Got it? 48 About $240 Estimate 42% of 120.**

Dante plans to put 80% of his paycheck into a savings account and spend the other 20%. His paycheck this week is $295. About how much will he put into his savings account? 48 About $240

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Example 3 Estimate 122% of % = 100% + 22% 100% of % of 50 (1 x 50) + (20% x 50) 50 + ( 1 5 x 50) = 60 So, 122% of 50 is about 60.

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Example 4 There are 789 seventh grader students at Washington Middle School. About 1 4 % of the 7th grade students have traveled overseas. What is the approximate number of 7th graders that have traveled overseas? Explain. 1 4 % can be estimated to 1%. 789 can be estimated to % x 800 = 0.01 x 800 = 8 8 x 1 4 = 2 So, about 2 seventh graders have traveled overseas.

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Got it? A country receives 3 4 % of a sales tax. About how much money would a country receive from the sale of a computer that costs $1,020? 3 4 % can be estimated to 1%. 1,020 can be estimated to % x 1000 = 0.01 x 1000 = x 3 4 = 7.5 So, it would cost about $7.50 in tax.

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Example 5 Last year, 639 students attended summer camp. Of those who attended this year, 0.5% also attended camp last year. About how many students attended the summer camp two years in a row? 0.5% is half of 1%. 1% of 639 ≈ 6 So, 0.5% of 639 is half of 6 or 3. About 3 students attended summer camp two years in a row.

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**The Percent Proportion**

Lesson 3

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**Use the Percent Proportion**

Type Example Proportion Find the Percent What percent of 5 is 4? Find the Part What number is 80% of 5? Find the Whole 4 is 80% of what number? 𝟒 𝟓 = 𝐧 𝟏𝟎𝟎 𝒑 𝟓 = 𝟖𝟎 𝟏𝟎𝟎 𝟒 𝒘 = 𝟖𝟎 𝟏𝟎𝟎 4 out of 5 is 80% 𝒑𝒂𝒓𝒕 𝒘𝒉𝒐𝒍𝒆 = 𝟒 𝟓 = 𝟖𝟎 𝟏𝟎𝟎

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**Find the percent. Let n represent the percent.**

Example 1 What percent $15 is $9? Ask: What type of percent proportion do you use? Find the percent. Let n represent the percent. In the table, the first number is the denominator and the second number in the numerator. 9 15 = 𝑛 100 9(100) = 15n 900 = 15n Divide 900 and 15. n = 60

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Got it? a. What percent of 25 is 20? 80% b. $12.75 is what percent of 4? 25.5%

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Example 2 What number is 40% of 120? 𝑝𝑎𝑟𝑡 𝑤ℎ𝑜𝑙𝑒 = 𝑝𝑒𝑟𝑐𝑒𝑛𝑡 100 𝑝 120 = p • 100 = 120 • p = 4800 p = 48 So, 48 is 40% of 120.

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Got it? a. What number is 5% of 60? 3 b. 12% of 85 is what number? 112

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Example 3 18 is 25% of what number? 𝑝𝑎𝑟𝑡 𝑤ℎ𝑜𝑙𝑒 = 𝑝𝑒𝑟𝑐𝑒𝑛𝑡 𝑤 = w • 25 = 18 • w = 1800 w = 72 So, 18 is 25% of 72.

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Got it? a. 40% of what number is 26? 65 b. 84 is 75% of what number? 112

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**Western Lowland Gorilla Diet**

Example 4 The average adult male Western Lowland gorilla eats about 33.5 pounds of fruit each day. How much food does the average adult male gorilla eat each day? Western Lowland Gorilla Diet FOOD PERCENT Fruit 67% Seeds, leaves, stems, and pith 17% Insects, insect larvae 16% 33.5 𝑤 = 33.5 •100 = w • 67 3350 = 67w 50 = w So, an average male gorilla eats 50 pounds of food each day.

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The Percent Equation Lesson 4

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Percent Equation Part = percent • whole 𝑝𝑎𝑟𝑡 𝑤ℎ𝑜𝑙𝑒 = _________________ 𝑝𝑎𝑟𝑡 𝑤ℎ𝑜𝑙𝑒 • whole = percent • _____________ ____________ = percent • whole percent whole part

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**Use the Percent Equation**

Type Example Proportion Find the Percent 3 is what percent of 6? Find the Part What number is 50% of 6? Find the Whole 3 is 50% of what number? 3 = n • 6 p = 0.5 • 6 3 = 0.5 • w 3 is 50% of 6 3 = x 6 part percent whole

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**Example 1 What number is 12% of 150?**

Do you need to find percent, part or whole? ________ part = 0.12 • 150 p = 18 So, 18 is 12% of 150. part

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**Write an equation and solve.**

Got it? 1 Write an equation and solve. b. Find 72% of 50. p = 0.72 • 50 p = 36 d. Find 50% of 70. p = 0.5 • 70 p = 35 a. What is 6% of 200? p = 0.06 • 200 p = 12 c. What is 14% of 150 p = 0.14 • 150 p = 21

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**Example 2 21 is what percent of 40?**

Do you need to find percent, part or whole? ________ 21 = n • 40 = n 0.525 = n So, 21 is 52.5% of 40. percent

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**Write an equation and solve.**

Got it? 2 Write an equation and solve. a. What percent of 40 is 9? 9 = n • % = n b. 27 is what percent of 150? 27 = n • % = n

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**Example 3 13 is 26% of what number?**

Do you need to find percent, part or whole? ________ 13 = 0.26 • w = w 50 = w So, 13 is 26% of 50. whole

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**Write an equation and solve.**

Got it? 3 Write an equation and solve. a. 39 is 84% of what number? 39 = 0.84 • w 46.4= w b. 26% of what number is 45? .26 = w • = w

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**About 13,056 people were surveyed.**

Example 4 A survey found that 25% of people aged gave up their home phone and only use a cell phone. If people only used a cell phone, how many people were surveyed? Do you need to find percent, part or whole? ________ 3,264 = 0.25w 13,056 = w About 13,056 people were surveyed. whole

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Percent of Change Lesson 5

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Percent of Change Words: A percent of change is the ratio that compares the change in quantity to the original amount. Equation: percent of change = amount of change original amount

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**Percent of Increase and Decrease**

Increase: percent of increase = amount of increase original amount Decrease: percent of decrease = amount of decrease original amount

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Example 1 Find the percent of change in the cost of gasoline from 1970 to Round to the nearest whole percent if necessary. This is a percent increase. It increased $1.65. percent of increase = amount of increase original amount = $1.65 $1.30 ≈ 1.27 or 127% The cost of gasoline increase by about 127% from 1970 to 2010.

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Example 2 Yusuf bought a DVD recorder for $280. Now it is on sale for $220. Find percent of change in the price. Round to the nearest whole percent if necessary. This is a percent decrease. It decreased by $60. percent of decrease = amount of decrease original amount = $60 $280 ≈ 0.21 or 21% The price of the DVD recorder decreased by about 21%.

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Got it? 1 & 2 a. Find the percent of change from 10 yards to 13 yards. 30% increase b. The price of a radio was $20. It is on sale for $15. What is the percent of change in the price of a radio? 25% decrease

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Percent Error Words: A percent error is a ratio that compares the inaccuracy of an estimate, or amount of error, to the actual amount. Equation: percent error = amount of error actual amount Suppose you guess there are 300 gum balls in the jar, and you guessed 400. amount of error actual amount = =0.25 or 25%

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**amount of error actual amount = 1.5 15 =0.1 or 10%**

Example 3 Ahmed wants to practice free-throws. He estimates the distance from the free-throw line to the hoop and marks it with chalk. Ahmed’s estimate was 13.5 feet. The actual distance should be 15 feet. Find the percent error. amount of error actual amount = =0.1 or 10% The percent error is 10%.

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**Sales Tax, Tips, and Markups**

Lesson 6

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Example 1 – Sales Tax Drew wants to buy exercise equipment that cost $140 and the sales take is 5.75%. What is the total cost? Add sales tax to the regular price. First, find the sales tax. Let t represent sales tax. t = x t = Next, add the sales tax to the regular price. $ = $148.05

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Example 1 – Sales Tax Drew wants to buy exercise equipment that cost $140 and the sales take is 5.75%. What is the total cost? Add the percent of tax to 100%. 100% % = % Let t represent sales tax. t = x t = $148.05 The total cost of the exercise equipment is $

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Got it? 1 What is the total cost of a sweatshirt if the regular price is $42 and the sales tax is %? $44.31

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Tips and Markups A tip or gratuity is a small amount of money in return for a service. The total price is the regular price of the service plus the tip. The store sells items for more than it pays for those items. The amount of increase is called the markup. The selling price is the amount the customer pays for an item.

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Example 2 A customer wants to tip 15% on a restaurant bill that is $35. What will be the total bill with the tip? Add sales tax to the regular price. First, find the tip. Let t represent the tip. t = x 35 t = Next, add the tip to the bill. $ $35 = $40.25

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Example 2 A customer wants to tip 15% on a restaurant bill that is $35. What will be the total bill with the tip? Add the percent of tip to 100%. 100% + 15% = 115% Let t represent the total. t = x 35 t = $40.25 Using either method, the total cost of the bill with tip is $40.25.

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Example 3 A haircut costs $20. Sales tax is 4.75%. Is $25 sufficient to cover the haircut with tax and a 15% tip? Sales tax and tip together is 19.75%. Let t represent the tax and tip. t = x t = $3.95 $20 + $3.95 = 23.95 Since $25 is more than $23.95, $25 would be enough.

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Got it? 2 & 3 a. Scott wants to tip his taxicab driver 20%. If his commute costs $15, what is the total cost? $18 b. Find the total cost of a spa treatment of $42 including a 6% tax and 20% tip. $52.92

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Example 4 A store pays $56 for a GPS navigation system. The markup is 25%. Find the selling price. First, find the markup. Let m represent the markup. m = x m = $14 $14 + $56 = $70 The selling price of the GPS is $70.

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Discount Lesson 7

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Vocabulary Discount or markdown is the amount by which the regular price of an item is reduced. The sales price is the regular price minus the discount.

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**Next, subtract the discount from the regular price.**

Example 1 A DVD normally costs $22. This week it is on sale for 25% off the original price. What is the sale price of the DVD? Subtract the discount from the regular price. First, find the amount of the discount. Let d represent the discount. d = x 22 d = Next, subtract the discount from the regular price. $22 - $5.50 = $16.50

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Example 1 A DVD normally costs $22. This week it is on sale for 25% off the original price. What is the sale price of the DVD? Subtract the percent of discount from 100%. 100% - 25% = 75% The sales price is 75% of the regular price. Let s represent sales price. s = x 22 s =

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Got it? 1 A shirt is regularly priced at $42. It is on sale for 15% off of the regular price. What is the sale price of the shirt? $35.70

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Example 2 A boogie board that has a regular price of $69 is on sale at a 35% discount. What is the price with 7% tax? Find the amount of the discount. Subtract the discount from the regular price. Let d represent the discount. $69 - $24.15 = $44.85 d = x d =

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**The sales price of the boogie board including tax is $47.99**

Example 2 A boogie board that has a regular price of $69 is on sale at a 35% discount. What is the price with 7% tax? The percent of tax is applied after the discount is taken. 7% of $44.85 = 0.07 • 44.85 = 3.14 $ $3.14 = $47.99 The sales price of the boogie board including tax is $47.99

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Got it? 2 A CD that has a regular price of $15.50 is on sale at a 25% discount. What is the sales price with 6.5% tax? $12.38

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Example 3 A cell phone is on sale for 30% off. If the sale price is $239.89, what is the original price? The sales price is 100% - 30% or 70% of the original price. Let p represent the original price. = x p = 0.7𝑝 0.7 = p The original price is $

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**The sales price at Ratcliffe’s is a better buy.**

Example 4 Clothes Are Us and Ratcliffe’s are having sales. At Clothes Are Us, a pair of sneakers is on sale for $40 off the regular price of $50. At Rattcliffe’s, the same brand of sneakers is discounted by 30% off of the regular price of $40. Which store has the better sale price? Clothes Are Us 60% of $50 = 0.6 x $50 = $30 The sales price is $30. Ratcliffe’s 70% of $40 = 0.7 x $40 = $28 The sales price is $28. The sales price at Ratcliffe’s is a better buy.

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Got it? 4 If the sales at Clothes Are Us was 50% off, which store would have the better buy? Clothes Are Us is cheaper $25 < $28

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**Financial Literacy: Simple Interest**

Lesson 8

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**Simple Interest Formula**

Words: Simple interest I is the product of the principal p, the annual interest rate, r, and the time t, expressed in years. Symbols: I = prt

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Example 1 Arnold puts $540 into a savings account. The account pays 3% simple interest. How much will he earn in each amount of time? a. 5 years I = prt I = 580 • 0.03 • 5 I = 87 He will earn $87 in interest in 5 years.

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Example 1 Arnold puts $540 into a savings account. The account pays 3% simple interest. How much will he earn in each amount of time? b. 6 months I = prt I = 580 • 0.03 • 0.5 I = 8.7 He will earn $8.7 in interest in 6 months.

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Got it? 1 a. Jenny puts $1,560 into a savings account. The account pays 2.5% simple interest How much interest will she earn in 3 years? $117 b. Marcos invests $760 into a savings account. The account pays 4% simple interest. How much interest will he earn after 5 years? $152

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Example 2 Rondell’s parents borrow $6,300 from the bank for a new car. The interest rate is 6% per year. How much simple interest will they pay if they take 2 years to repay the loan? I = prt I = 6,300 • 0.06 • 2 I = 756 Rondell’s parents will pay $756 in interest in 2 years.

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Example 3 Derrick’s dad bought new tires for $900 using a credit card. His card has an interest rate of 19%. If he has no other charges on his card and does not make a payment, how much money will he owe after one month? I = prt I = 900 • 0.19 • 𝟏 𝟏𝟐 I = $900 + $14.25 = $ The total amount owed is $

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Got it? 2 a. Mrs. Hanover borrows $1,400 at a rate of 5.5% per year. How much simple interest will she pay if it takes 8 months to repay the loan? $51.33 b. An office manager charged $425 worth of office supplies on a credit card. The credit card has an interest rate of 9.9%. How much money will he owe at the end of one month if he makes no other charges on the card and does not make a payment? $428.51

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Example 4 Luis is taking out a car loan for $5,000. He plans on paying off the car loan in 2 years. At the end of 2 years, Luis will have paid $300 in interest. What is the simple interest rate on the car loan? I = prt 300 = 5000 • r • 2 300 = 10,000r 𝟑𝟎𝟎 𝟏𝟎,𝟎𝟎𝟎 = 𝟏𝟎,𝟎𝟎𝟎𝒓 𝟏𝟎,𝟎𝟎𝟎 r = 0.03 or 3%

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Got it? 4 Maggie is taking out a student loan for $2,600. She plans on paying off the loan in 3 years. At the end of 3 years, Maggie will have paid $390 in interest. What is the simple interest rate on the student loan? 5%

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