An investment of $2000 in a bank account doubles every five years. The function that models the growth of this investment is f(x)=2000•2^x, where x is the number of doubling periods, or 10 years?
x=1 after the first 5 years; x=2 after the another 5 years (or better said after the first 10 years in the bank); x=3 after another 5 years ( or better said after the first 15 years in the bank) and so on...
x is the number of 5 years intervals which have passed up to a moment in time :)
