Sharp EL-531RH Teachers Manual page 37

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 100 years.
Press the following buttons and then start operation.
The original amount, or principal, is $100; so a = 100.
The number of years is 100; so n = 100.
The interest is 0.1%; so x = 1.001.
100 1.001
You have $110.50 after 100 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...
Divide both sides by 'a'
Calculates the 'log' of both sides
If 'a' is the money deposited, the savings would double.
2
It takes approximately 694 years for your money to double.
100
n
ax
n
x = 2
log x
nlogx = log2
n = log2/logx
1.001
36
100X1.001^10
= 2a
n
= log2
log2 log1.00
Junior high school
DEG
DEG