What is the simple interest rate per annum on an investment that took up to 12.5 years to double its initial amount?  Choose the most appropriate option.
A) 10  B) 6  C) 12  D) 4  E) 8
P = (P*SI*12.5)/100   100P = P*SI*12.5   100 = 12.5SI   Therefore SI = 8%   8= 8
<result>E</result>
What is the simple interest rate per annum on an investment that took up to 12.5 years to double its initial amount?