Runtime multiplication

HI, I have a products model and a dealers model . I am creating an app in which a dealer selects a product and then he's routed to purchase order form . I want to create a dynamic multiplication of Produc开发者_运维问答ts*Price = Total price i.e. when the form opens , he adds the quantity of the product and the default price is multiplied with no. of products to give total price.

What shall I do ?

Please guide. Thanks

There are a lot of good guides out there for Rails 3 and Unobtrusive Javascript (UJS). Here's one that starts you from the ground up:

http://net.tutsplus.com/tutorials/javascript-ajax/using-unobtrusive-javascript-and-ajax-with-rails-3/