If the simple interest on a certain sum of money after 3 1/8 years is 1/4 of the principal, what is the rate of interest per annum?
A sum of Rs. 725 is lent in the beginning of a year at a certain rate of interest. After 8 months, a sum of Rs. 362.50 more is lent but at the rate twice the former. At the end of the year, Rs. 33.50 is earned as interest from both the loans. What was the original rate of interest?