36
Junior high school
A Question of Interest
For High school Students
How much will your investment be worth in n years?
Let’s make an equation.
The original amount of money invested, called the principal, multiplies each year by the
amount x.
Let’s use this equation to see how much money we have after
1
00 years.
The original amount, or principal, is $
1
00; so a =
1
00.
The number of years is
1
00; so n =
1
00.
The interest is 0.
1
%; so x =
1
.00
1
.
1
00
1
.00
1
1
00
You have $
11
0.50 after
1
00 years.
How many years would it take for the money to double?
Let’s make an equation.
The money invested multiplies each year by the amount x.
After n years the money doubles, so...
ax
n
= 2a
Divide both sides by ‘a’
x
n
= 2
Calculates the ‘log’ of both sides
log x
n
= log2
nlogx = log2
n = log2/logx
If ‘a’ is the money deposited, the savings would double.
2
1
.00
1
It takes approximately 694 years for your money to double.
Press the following buttons and then start operation.
100X1.001^10
DEG
log2
÷
log1.00
DEG
Summary of Contents for EL-531RH
Page 1: ...SCIENTIFIC CALCULATOR TEACHER S GUIDE JULY 1999 EL 531RH ...
Page 56: ......
