Question

In the year 2000, there were 200,000 cell phone subscribers in a city in New York. The number of subscribers increased by 60 percent per year after 2000. Which equation can be used to model the number of subscribers, y, in the city t years after 2000?
A) y=200,000(1+60)t
B) y=200,000(1+0.6)t
C) y=200,000(1-60)t
D) y=200,000(1-0.6)t

Answer 1

The first step is to calculate the percentage increase for each year.
If the subscribers increase by 60%, it means that the subscribers will be (100+60)% of the previous year. 

(100+60)% = (100/100 + 60/100)
                     (1 + 0.6)

After 2,000, the subscribers will be 200,000×(1+0.6).
For the following years the 200,000×(1+0.6)t

So, the value of y will be given by,

Y=200,000(1+0.6)t