If I have $4,000 and earn 4% a month how long will it take me to have $20,000

Question

This is a math problem that I do not know how to set up or solve.

Answer 1

 

100% +r = 100% + 4% = 104% = 1.04

 

P = (1+r)^t where principal P=4000

 

4000 ( 1.04)^t = 20000

 

1.04^t = 5

 

log 1.04^t = log 5

 

t * log 1.04 = log 5

 

t = log 5 / log 1.04 = 41.0354

 

42 months = 3 and 1/2 years = 3 years and 6 months