At what rate percent of simple interest will a sum of money double itself in 20 years?

The simple interest on Rs. 1820 from March 9, 2003 to May 21, 2003 at 7 1⁄2% rate is

Arun borrowed a sum for 4 years on S.I. at 12%. The total interest paid was Rs. 360. Find the Principal.

The simple interest on Rs.500 at 6% per annum from May 3rd to July 15th in the same year is

A sum was put a simple interest at a certain rate for 2 years. Had it been put at 4% higher rate, it would have fetched Rs. 60 more. The sum is:

A sum of money becomes $\dfrac{7}{5}$ of itself in 4 years at a certain rate of simple interest. The rate per annum is :

If the simple interest on Rs. 2000 is less than the Simple Interest on Rs. 3000 at 5% by Rs. 50, find the time.

On May 30,2012 a businessman loans $15,000 in the bank for the expansion of his restaurant.it was agreed that he will pay the amount with 6% rate of interest on August 10,2012.what is the ordinary simple interest to be paid?

Louie borrowed $1800 from his aunt last December 25,2010.He promised that he will pay his aunt on February 14,2011 at 8% interest.Find the exact simple interest to be paid by Louie.

An employee loans $800 from the labor union and promised to pay the amount in 1 year .How much will he need to pay after 1 year if the interest rate is 15%?