2.9 PERCENTSI can solve percent problems using proportions or the percent equation.

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:

USING PROPORTIONS

What percent of 50 is 25? Use a proportion.

Cross product So 2500 = 50p 50 = p 50%

PRACTICE

What percent of 56 is 42? 75%

What percent of 90 is 54? 60%

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%

PRACTICE

Using the percent equation, what percent of 30 is 18? 60%

What percent of 56 is 35 62.5%

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

FINDING A BASE

125% of what number is 17.5? 17.5 = 125% ∙ b 17.5 = 1.25 ∙ b

14 = b

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

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

ASSIGNMENT

ODDS ONLY P.141 #9-29