How can a model help
you visualize finding
a p a rt o r base?
Use th e m odel b e lo w to
help you visualize finding
the part in the equation
a = 30% • 38.50.
Pr o b l em 3 Finding a Part
Shopping A dress shirt that normally costs $38.50 is on sale for 30% off. What is the
sale price of the shirt?
Step 1 Use th e p e rc e n t e q u a tio n to find th e a m o u n t of discount.
a = p% • b Write the percent equation.
= 30% • 38.50 Substitute 30 fo r p and 38.50 fo r b.
= 0.30 • 38.50 Write the percent as a decimal.
= 11.55 Multiply.
Step 2 Find th e sale price.
$ 3 8 .5 0 -$ 1 1 .5 5 = $26.95
The sale price of th e shirt is $26.95.& G o t It? 3. A family sells a car to a dealership for 60% less th a n they p aid for it. They
p aid $9000 for th e car. For w h at price did they sell th e car?ik
Will 125% of a
number be greater
than the number?
Yes. W hen you m u ltip ly
a p o s itiv e n u m b e r by
a p e rce n t g re a te r th a n
100 %, the part w ill
be greater th a n th e
base, as s h o w n in th e
model below.
0
0 %b 17.5100% 125%Pr o b l em 4 Finding a Base
125% of what number is 17.5?
a = p% • b
17.5 = 125% • b
17.5 = 1.25 • b
14 = b125% of 14 is 17.5.Write the percent equation.
Substitute 17.5 for a and 125 for p.
Write the percent as a decimal.
Divide each side by 1.25.*£ Got It? 4. 30% of w hat n u m b e r is 12.5? Solve th e p roblem using th e p ercen t equation.
Then solve th e p ro b lem using th e p ercen t proportion.A co m m o n application of percents is sim ple interest, w hich is interest you ea rn on only
th e principal in an account.Key Concept Simple Interest Formula
The sim ple interest form ula is given below, w here I is th e interest, P is th e principal,
r is th e an n u al interest rate w ritten as a decim al, a n d t is th e tim e in years.
Algebra / = Prt
Example If you invest $50 at a sim ple interest rate of 3.5% p e r y ear for 3 years, the
interest you ea rn is 1= 50(0.035)(3) = $5.25.PowerAlgebra.com | Lesso n 2- 9 Percents^139