Warm-up
Three quick questions from earlier lessons.
Discover
A 60-dollar coat is 10% off. What do you pay?
- 54 dollars
- 6 dollars
Key idea
Increase: add; decrease: subtract, always a percent of the original.
An increase of gives of the original; a decrease gives . Tax and tips are increases, discounts are decreases. Percent change = change ÷ original × 100.
Worked example
Price from 40 to 46 dollars.
Change.
, a 15% increase
6 ÷ 40.
Your turn, guided
Your turn: 80 dollars plus 5% tax. The total.
80 · 1.05.
Practice ★
- A 160-dollar jacket's price goes up by 40%. What is the new price (dollars)?
- A 300-dollar jacket's price goes up by 20%. What is the new price (dollars)?
- A 320-dollar game is 35% off. What is the sale price (dollars)?
Watch out!
Practice ★★
- A town grew from 280 to 518 people. By what percent did it grow?
- A town grew from 260 to 468 people. By what percent did it grow?
- Boss problem. A meal costs 120 dollars. The sales tax is 10% and you leave a 20% tip on the price before tax.
Exit ticket
Three questions to check you have got it.
- A 160-dollar jacket's price goes up by 40%. What is the new price (dollars)?
- A 300-dollar jacket's price goes up by 20%. What is the new price (dollars)?
- A 60-dollar jacket's price goes up by 60%. What is the new price (dollars)?
Summary card
Percent increase and decrease
New = of the original; change ÷ original for the percent.
Watch out: the base is the original amount.