Suppose $100 is deposited into an account and the amount doubles every 8 years. How much will be in the account after 40 years?

Question

Need to know an equation 

Answer 1

You need a formula. OK. Let

 

PV = present value (how much you start with)

FV = future value (how much you end up with)

n   = how many years you have the money deposited

N   = how many years it takes for the money to double (8 in this case)

 

Then

 

FV = 2^(n/N) PV

 

For your case, n=40, N=8, PV=100 so it doubles five times.

 

FV = 32 (100) = 3200

 

Oh, the power of compound interest. Start saving while you're young. :-)

Answer 2

A(t) = ($100)*2^t/8

 

A(t=40) = ($100)*2^40/8 = ($100)*2⁵ = ($100)*(32) = $3200