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Finding Percent of Change

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Finding Percent of Change

Percent of Change

- Percent of Change – the percent a quantity increases or decreases from the original amount

- Step 1 – Subtract to find the amount of change

- Step 2 – Use the proportion

Amount of change = Percent of change

Original amount 100

Percent of Change - Increase

- North Carolina had 12 seats in the U.S. House of Representatives in the 1990’s. After the 2000 census, North Carolina had 13 seats. Find the percent of increase in the number of representatives.

- Step 1 – Subtract to find the amount of change

13 seats - 12 seats = 1 seat change

- Step 2 – Use the proportion

Amount of change = Percent of change

Original amount 100

1= x

12 100

=

1 (100)

12 x

=

100

12 x

12

12

=

8.3%

x

- A restaurant worker earning $5.15 an hour receives a raise. He now earns $6.00 and hour. Find the percent of increase in his hourly rate of pay.

- Step 1 – Subtract to find the amount of change

$6.00 - $5.15 = $0.85 increase per hour

- Step 2 – Use the proportion

Amount of change = Percent of change

Original amount 100

$0.85= x

$5.15 100

=

0.85 (100)

5.15 x

=

85

5.15 x

5.15

5.15

=

16.5%

x

- Vincent collects dinosaurs. Before his birthday he had 16 dinosaurs. After his birthday party, he had a total of 40 dinosaurs. Find the percent of increase in the number of dinosaurs Vincent has.

- 40 - 16 = 24 dinosaurs

Amount of change = Percent of change

Original amount 100

24= x

16 100

=

24(100)

16 x

=

2400

16 x

16

16

=

150%

x

Percent of Change: Decrease (discount)

- During a clearance sale, a keyboard that normally sells for $49.99 is discounted to $34.99. What is the percent of discount?

- Step 1 – Subtract to find the amount of change

$49.99 - $34.99 = $15.00 discount

- Step 2 – Use the proportion

Amount of change = Percent of change

Original amount 100

$15.00= x

$49.99 100

=

15 (100)

49.99 x

=

1500

49.99 x

49.99

49.99

=

30%

x

- Due to the number of infractions given, the number of students able to attend the Mardi Gras Mania decreased from 206 students to 180 students. What is the percent of decrease?

- 206 - 180 = 26 students

Amount of change = Percent of change

Original amount 100

26= x

206 100

=

26 (100)

206 x

=

2600

206 x

206

206

=

12.62%

x

Percent of Change: Markup

- An electronic store orders sets of walkie-talkies for $14.85 each. The store sells each set for $19.90. What is the percent of markup?

- Step 1 – Subtract to find the amount of markup

$19.90 - $14.85 = $5.05 markup

- Step 2 – Use the proportion

Amount of markup = Percent of change

Original cost 100

$5.05= x

$14.85 100

=

5.05 (100)

14.85 x

=

505

14.85 x

14.85

14.85

=

34%

x

- Macy’s spends $30.72 on Polo shirts. They then sell the shirt for $55.84. What is the percent of markup on the Polo shirts?

- $55.84 - $30.72 = $25.12

Amount of markup = Percent of change

Original cost 100

25.12= x

30.72 100

=

25.12 (100)

30.72 x

=

2512

30.72 x

30.72

30.72

=

81.77%

x

Finding the Original

- How do we find the original price when we know the discounted price and the percent off?

- Watch Example Video

- Step one – Find the percentage you are paying by subtracting 100% - the percent off

- Step two – divide the discounted price by the percent you are paying

- A shirt is on sale for 40% off. The sale price is $12. What is the original cost of the shirt?

- Step 1: 100% - percent off = percent still paying for

100% - 40% = 60%

- Step 2: sale price ÷ % paying for = original price

12 ÷ .60 = $20.00

- A television is on sale for 30% off. The sale price is $425. What is the original cost of the television?

- Step 1: 100% - percent off = percent still paying for

100% - 30% = 70%

- Step 2: sale price ÷ % paying for = original price

425 ÷ .70 = $607.14

- A car is on sale for 20% off. The sale price is $12,375. What is the original cost of the car?

- Step 1: 100% - percent off = percent still paying for

100% - 20% = 80%

- Step 2: sale price ÷ % paying for = original price

$12,375 ÷ .80 = $15,468.75

Homework Time! Luck of the Irish To You!