Question 1160813
8000=4000(1+(.04/4))^4t, where t is number of years
2=(1+0.01)^4t
ln both sides
ln 2=4t ln 1.01 rule of log
t=ln2/(4 ln(1.01)
=17.42 years

Rule of 70
70/rate in percent = time in years to double.
Here, it would yield 70/4=17.5 years.