simple_interest.notebook
Essential Question:
When is interest a positive thing and
when is it a negative thing?
February 15, 2013
Simple Interest:
I=prt
Remember Puddle: percent to decimal move
left 2 places
Jan 30­3:24 PM
Jan 28­4:42 PM
Jan 28­4:42 PM
Jan 28­4:43 PM
http://www.math­play.com/Simple­Interest/Simple­Interest.html
Jan 31­3:08 PM
What do you do if you are given
the interest and you are asked to
find principal, rate, or time?
Jan 31­2:31 PM
1
simple_interest.notebook
February 15, 2013
Robin has $2,500 to invest in a CD (certificate of deposit)
1. If Robin invests the $2,500 in the CD that yields 4%
interest, what will the CD be worth after 2 years?
2. Robin would like to have $3,000 altogether. If the interest
rate is 5%, in how many years will she have $3,000?
Extension Activity:
We are going to take what we know about
finding simple interest and use an Excel
program to help us.
We can tell Excel what to do to find the
interest as well as a total amount.
3. Suppose Robin invests the $2,500 for 3 years and earns
$255. What was the rate of interest?
Jan 31­2:37 PM
Feb 11­9:51 AM
When using Excel, there are
important words/phrases that you
need to understand.
column: up and down/vertical
Labeled A B C D E etc.
row: left to right/ horizontal
Labeled 1 2 3 4 5 etc.
tab (down vs over)
cell: where a row and column intersect;
Ex: A1, B8
The = sign is important-every
formula starts with =
the asterisk * means multiply
and the / means divide.
Feb 11­9:58 AM
Feb 11­3:38 PM
I=prt
principal
$750 rate
7% rate
time
$750 7% 3 yrs
3 yrs
$750
3.5% 3 yrs 7% 1.5 years time
principal
interest
total
$1,200 3.5% 2 yrs $750
$450 5% 4 months $750
?% 3 yrs 7% ? years $1,000 2% 9 months $750
$600
8% 1 month $750 .7% $2,500
6.9% 6 months $750 7% $2,000 20% 1 yr interest
total
3 years
3 months Use what we have shown you with Excel to find the interest
earned as well as what the total amount would be in an account
once you have found the interest.
Remember time in months must be expressed as a decimal, but we
can use a formula in excel.
Feb 11­9:53 AM
Feb 13­3:21 PM
2
simple_interest.notebook
February 15, 2013
Now solve the following problems using Excel. Write down
the steps you used in excel. In addition to finding the
interest, find the total amount including interest.
Steps:
Interest:
Total:
Steps:
Interest:
Total:
Jan 28­4:43 PM
Jan 28­4:43 PM
Summary
Simple Interest
________________________________
________________________________
________________________________
________________________________
________________________________
Dec 21­11:24 AM
Jan 31­2:36 PM
Feb 14­11:16 AM
3