Question 1054967
the formula for simple interest is i * p * n.


i is the interest rate per time period.
p is the principal.
n is the number of time periods.


the formula for future value of an investment using simple interest is f = p + p * i * n).


this can be simplified to f = p * (1 + i * n).


you are given that n = 13 years.
you will be looking for the interest rate per year.
since you will be quadrupling your money, than f will be equal to 4p.


your formula of f = p * (1 + i * n) becomes:


4p = p * (1 + 13 * i)


divide both sides of this equation by p to get:


4 = 1 + 13 * i


subtract 1 from both sides of this equation to get:


3 = 13 * i


divide both sides of this equation by 13 to get:


3/13 = i


that's your interest rate per year.


i = 3/13 = .2307692308


for example:


assume your principal is equal to 500 dollars.


your interest in 13 years will be equal to 500 * 3/13 * 13 which will become 500 * 3 which will become 1500 dollars.


add that to your principal of 500 dollars and you get a total of 2000 dollars which is equal to 4 times the original investment of 500 dollars.