# Percent Increase and Decrease

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Percent Increase and Decrease
2-10 Percent Increase and Decrease Holt Algebra 1 Warm Up Lesson Presentation Lesson Quiz

Warmup: Which is a better deal?
Get Your Calculator Warmup: Which is a better deal? A DVD costs \$20. Sales tax is 8% and you receive a 10% discount. Should you calculate the tax first then the discount or the other way around?

Discount first: (\$20)(.10) = \$2 20 – 2 = \$18 Tax first: (\$20)(.08) = \$1.60 = \$21.60 Now Discount: (\$21.60)(.10) = \$2.16 21.60 – 2.16 = \$19.44 Now Tax: (\$18)(.08) = \$1.44 = \$19.44 Which is a better deal for you? Which is a better deal for the business?

Warm Up 1. Find 30% of 40. 2. Find 28% of 60. 12 Solve for x.
5. 20 is what percent of 80? 6. 36 is what percent of 30? 12 16.8 0.44 38 25% 120%

Objective Find percent increase and decrease.

Vocabulary percent change percent increase percent decrease discount
markup

A percent change is an increase or decrease given as a percent of the original amount. Percent increase describes an amount that has grown and percent decrease describes an amount that has be reduced. Notes on next slide

Definition: (write this down)
Percent of Change Definition: (write this down) Percent of Change = Difference Original Which Means: % Increase or % Decrease Using this formula, your answer comes out as a decimal. Just multiply by 100 to change to a percent

Example 1A: Finding Percent Increase and Decrease
Find each percent change. Tell whether it is a percent increase or decrease. From 8 to 10 Simplify the numerator. Simplify the fraction. = 0.25 = 25% Write the answer as a percent. 8 to 10 is an increase, so a change from 8 to 10 is a 25% increase.

Helpful Hint Before solving, decide what is a reasonable answer. For Example 1A, 8 to 16 would be a 100% increase. So 8 to 10 should be much less than 100%.

Example 1B: Finding Percent Increase and Decrease
Find the percent change. Tell whether it is a percent increase or decrease. From 75 to 30 Simplify the fraction. Simplify the numerator. = 0.6 = 60% Write the answer as a percent. 75 to 30 is a decrease, so a change from 75 to 30 is a 60% decrease.

Example 2: Finding Percent Increase and Decrease
A. Find the result when 12 is increased by 50%. 0.50(12) = 6 Find 50% of 12. This is the amount of increase. =18 It is a percent increase, so add 6 to the original amount. 12 increased by 50% is 18. B. Find the result when 55 is decreased by 60%. Find 60% of 55. This is the amount of decrease. 0.60(55) = 33 55 – 33 = 22 It is a percent decrease so subtract 33 from the the original amount. 55 decreased by 60% is 22.

Common application of percent change are discounts and markups.
A discount is an amount by which an original price is reduced. discount = % of original price final price = A markup is an amount by which a wholesale price is increased. final price = wholesale cost markup + = % of

Example 3: Discounts The entrance fee at an amusement park is \$35. People over the age of 65 receive a 20% discount. What is the amount of the discount? How much do people over 65 pay? Method 1 A discount is a percent decrease. So find \$35 decreased by 20%. Find 20% of 35. This is the amount of the discount. 0.20(35) = 7 35 – 7 = 28 Subtract 7 from 35. This is the entrance fee for people over the age of 65.

Example 3A: Discounts Method 2 Subtract the percent discount from 100%. 100% – 20% = 80% People over the age of 65 pay 80% of the regular price, \$35. 0.80(35) = 28 Find 80% of 35. This is the entrance fee for people over the age of 65. 35 – 28 = 7 Subtract 28 from 35. This is the amount of the discount. By either method, the discount is \$7. People over the age of 65 pay \$28.00.

Helpful Hint Before solving, decide what is a reasonable answer. For example 3A, a 10% discount is \$3.50 off. So a 20% discount would be more than \$2 off.

Example 3B: Discounts A student paid \$31.20 for art supplies that normally cost \$ Find the percent discount . Think: is what percent of 52.00? Let x represent the percent. \$52.00 – \$31.20 = \$20.80 20.80 = x(52.00) Since x is multiplied by 52.00, divide both sides by to undo the multiplication. 0.40 = x 40% = x Write the answer as a percent. The discount is 40%

Example 4: Markups The wholesale cost of a DVD is \$7. The markup is 85%. What is the amount of the markup? What is the selling price? Method 2 Method 1 A markup is a percent increase. So find \$7 increased by 85%. Add percent markup to 100% Find 85% of 7. This is the amount of the markup. 100% + 85% = 185% The selling price is 185% of the wholesale price, 7. 0.85(7) = 5.95 1.85(7) = 12.95 = 12.95 Find 185% of 7. This is the selling price. Add to 7. This is the selling price. 12.95  7 = 5.95 Subtract from This is the amount of the markup. By either method, the amount of the markup is \$5.95. The selling price is \$12.95.

Lesson Quiz: Part 1 Find each percent change. Tell whether it is a percent increase or decrease. 1. from 20 to 28. 2. from 80 to 62. 3. from 500 to 100. 4. find the result when 120 is increased by 40%. 5. find the result when 70 is decreased by 20%. 40% increase 22.5% decrease 80% decrease 168 56

Lesson Quiz: Part 2 80% decrease 1. from 500 to 100. 168
Find the percent change. Tell whether it is a percent increase or decrease. 80% decrease 1. from 500 to 100. 2. find the result when 120 is increased by 40%. 168 Find each percent change. Tell whether it is a percent increase or decrease. 3. A movie ticket costs \$9. On Mondays, tickets are 20% off. What is the amount of discount? How much would a ticket cost on a Monday? 4. A bike helmet cost \$24. The wholesale cost was \$15. What was the percent of markup? \$1.80; \$7.20 60%