# Math Help - Compound discount question

1. ## Compound discount question

Edit: I have figured out how to solve this problem

"An account with initial amount $B earns compound interest at an annual effective interest rate i. The interest in the third year is$426, and the discount in the seventh year is \$812. Find i."

I know how to solve this problem with a graphing calculator or program that can solve variables, but I'm only allowed to use a regular calculator on the upcoming test. How can I set up the equations in this problem to solve for i in a minimal amount of time?

2. $
F = P\left( {1 + i} \right)^n \Leftrightarrow i = \left( {\frac{F}
{P}} \right)^{\frac{1}
{n}} - 1 = \sqrt[n]{{\frac{F}
{P}}} - 1
$

3. Thank you for trying to help, but what you posted is already familiar to me.

My problem is trying to set up a system of equations from which I can solve for i on paper (a numerical answer for i). I can't find a strategy to solve that works on paper without taking a very very long time.