Display a percentage of the final price

Hi

On the product details page, how can I display a fraction of the final price (this final price is calculated with the options added by another extension) ?

On each product page, I would like to inform the client that he can pay in 3 times without fee.

So, just below the price, I need to display for ex "In 3 times without fee" : 200 €, for a product price of 600€, 200€ being calculated automatically, of course (final price / 3).

It's just an information for the customer. The real selection of a payment in 3 times will be done and the end of the order validation.