2.9 Percents

1. 2.9 Percents I can solve percent problems using proportions or the percent equation.

2. The percent proportion • “a is p percent of b” • In this proportion, b is the base and a is a part of the base. • So here is the proportion:

3. Using proportions • What percent of 50 is 25? • Use a proportion. • Cross product • So 2500 = 50p • 50 = p • 50%

4. Practice • What percent of 56 is 42? • 75% • What percent of 90 is 54? • 60%

5. The percent equation • a = p% ∙ b • Ex: what percent of 40 is 2.5? • 2.5 = p% ∙ 40 • Solve for p • 0.0625 = p% • 6.25% = p%

6. Practice • Using the percent equation, what percent of 30 is 18? • 60% • What percent of 56 is 35 • 62.5%

7. Finding A pART • A dress shirt that normally costs $38.50 is on sale for 30% off. What is the sale price? • a = 30% ∙ 38.50 will tell you how much is taken off • Or you can use a = 70% ∙ 38.50 to tell what the price will be • $26.95

8. Finding a base • 125% of what number is 17.5? • 17.5 = 125% ∙ b • 17.5 = 1.25 ∙ b • 14 = b

9. Simple interest formula • Simple interest is a common application of percents. • I = interest • P = the principal (what you started with) • r = the annual interest rate • t = time in years

10. Example • If you invest $50 at a simple interest rate of 3.5% per year for 3 years, what is the amount of interest earned? • I = this is what we’re solving for • P = 50 • r = 3.5% = 0.035 • t = 3 • I = $5.25

11. Assignment • ODDS ONLY • P.141 #9-29