I'm looking at a way that I can solve the following issue.
If I borrow £1000 from a lender, and the interest rates we're different dependent on the value. How could I work out the total interest percentage regardless of the amount being lended?
For instance, say I have the following interest rates
Amount borrowed / Interest
£0 - £100 : 10%
£100 - £500: 20%
£500 - £1000: 30%
I want to borrow £1000, I would have the first £100 charged at 10% interest, then the next £400 would be 20% interest, and final £500 would be 30%.
Is there a formula that exists that could tell me the final combined interest rate? and would this formula work if I wanted to borrow say £400