美國的SAT數學exam

A business paid $300 to rent a piece of office equipment for one year . The rent was then increased by 10 percent each year thereafter. How much will the company pay for the first three years it rents the equipment?
有兩個方法，視乎你想應用哪種概念。
１．使用簡單年利計算：
－－－－－－－－－－－
First year price
= $300
Second year price
= First year price * (1+10%)
= $300 * (110%)
= $300 * 1.1
= $330
Third year price
= Second year price * (1+10%)
= $330 * (110%)
= $330 * 1.1
= $363
Total price
= $300 + $330 + $363
= $993
２．使用等比數列計算：
－－－－－－－－－－－
First term a
= $300
Common ratio r
= 110%
= 1.1
NUmber of terms n
= 3
Geometric Sum
= a[1-rn]/(1-r)
= $300[1-1.1³]/[1-1.1]
= $300[1-1.331]/(-0.1)
= $300(3.31)
= $993
So the total price is $993.