Question 998632
rule of 72: doubles in 72/13; 72 divided by interest rate which would be about 5.54 years.The rule of 72 slightly overestimates the time to double.  It applies in this case.
P=Poexp^rt
P/Po=2, which is doubling.
2=exp^rt
ln 2=rt
ln2/r=t
0.693/0.13 =t
t=5.33 years