7th Grade Math

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Applying Percents

PART A BCDEF

Multi-Part

Lesson 3

GLE 0706.2.4

Use ratios, rates and

percents to solve single-

and multi-step problems

in various contexts. Also

addresses GLE 0706.1.8.

Main Idea

Use a spreadsheet to

calculate simple

interest.

Spreadsheet:

Simple Interest

A computer spreadsheet is a useful tool for quickly calculating simple

interest for different values of principal, rate, and time.

SAVINGS Joel plans on opening a “Young Savers” account at his

bank. The current rate on the account is 4%. To find the balance

at the end of 2 years for different principal amounts, he enters

the values B2 = 4 and C2 = 2 into the spreadsheet below.

T

1

4

3

2

5

6

7

8

Simple Interest

Principal (p)

=B2/100

=B2/100

=B2/100

=B2/100

=B2/100

=C2

=C2

=C2

=C2

=C2

=A3*B3*C3

=A4*B4*C4

=A5*B5*C5

=A6*B6*C6

=A7*B7*C7

=A3+D3

=A4+D4

=A5+D5

=A6+D6

=A7+D7

500

1000

1500

2000

2500

Rate (r) Time (t) Interest (I) New Balance

Sheet 1 Sheet 2 Sheet 3

ABCD E

For each principal given in column A, simple

interest is calculated for any values of rate and

time entered in B2 and C2, respectively.

The spreadsheet

adds simple interest

to the principal.

the Results

1. Why is the rate in column B divided by 100?


2. What is the balance in Joel’s account after 2 years if the principal
   is $1,500 and the simple interest rate is 4%?


3. How much interest does Joel earn in 2 years if his account has a
   principal of $2,000 and a simple interest rate of 4%?


4. Is the amount of principal proportional to the interest Joel earns if
   his account earns 4% simple interest over 2 years? Explain.


5. Is the amount of principal proportional to the balance in Joel’s
   account if it earns 4% simple interest over 2 years? Explain.

Lesson 3F Applying Percents 363

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