Algebra I
posted by Cat on .
...excess information....
The historical society tells him that furniture similar to his has been appreciating in value at 10% per year for the last 20 years and that his furniture could be worth $10,000 now.
Is my expression 10,000(1+.1)^x?
If so, I have to find what it costed 20 years ago. Would I just raise the expression to the power of 20, or 20?

no
let the amount that it "costed" 20 years ago be x
then x(1.1)^20 = 10000
x = 10000/(1.1^20)
I get 1486.44
you might have seen the formula
Present Value = amount (1+i)^n
then Present value = 10000(1.1)^20
= 1486.44
If you know about negative exponents you will realize that the two equations are the same. 
A new machine was purchased at the beginning of one year for $200. Each year the machine loses value. It is worth 90% as much as the previous year. What is the value of the machine at the end of the 4th year.