Algebra 1 Common Core Student Edition, Grade 8-9

W hen you solve p roblem s involving percents, it is helpful to know fraction

equivalents for com m on percents. You can use th e fractions to check your answ ers for

reasonableness. Here are som e com m on percents re p resen te d as fractions.

1% 100 5% 2Q^10 % = i^20 % = | 25% = |

33.3% = I 50% = \^66.^6 % = | 75% = |^100 % =^1

Problem 5 Using the Simple Interest Formula

Finance You deposited $840 in a savings account that earns a simple interest rate

of 4.5% per year. You want to keep the money in the account for 4 years. How much

interest will you earn? Check your answer for reasonableness.

This is a s im p le in te re s t p ro b le m , so use th e

form ula fo r simple interest.

Write

I = Prt

Identify w h a t you know from the problem:

P = 840, r = 0.045, and t = 4.

Check for reasonableness by using a

c o m m o n percent. Since 4 .5 % is a b o u t 5% ,

use 5%.

= 840(0.045)(4)

/

= 151.2

The account will earn $151.20.

840 • ^ • 4 = 42 • 4 = $168

So, $151.20 is reasonable.

* G o t It? 5. You d eposited $125 in a savings acco u n t th a t earns a sim ple interest rate of

1.75% p er year. You e a rn ed a total of $8.75 in interest. For how long was your

money in the account?

Concept Sum m ary Solving Percent Problems

Problem Type Example Proportion Equation

Find a percent. W hat p ercen t of 6.3 is 3.5? |= | = ^ 3.5 = p% • 6.3

Find a part. W hat is 32% of 125? i t s = M a = 32% * 125

Find a base. 25% of w hat n u m b e r is 11? 11 = 25% • b

140 Ch ap t er 2 So l v i n g Eq u a t i o n s