Rule of 70
Suppose you invest $100 at 3%
compounded monthly. How long will it
take to double your money?
Now, since 
. We want to find t so that,
200 = 100[(1.0025)12t]
2 = (1.0025)12t
ln 2 = 12t[ln
1.0025]
t = 
Rule of 70
Suppose you invest $100 at 3%
compounded monthly. How long will it
take to double your money?
Now, since . We want to find t so that,
200 = 100[(1.0025)12t]
2 = (1.0025)12t
ln 2 = 12t[ln
1.0025]
t =