how to redirect root to index.aspx

I'm trying to come up with a rule to redirect requests to a root folder to go to index.aspx

example:  http://site.com/folder1  -> http://site.com/folder1/index.aspx

or   http://site.com/folder1/  -> http://site.com/folder1/index.aspx

User may or may not type a / after the folder name, but i always want them to redirect to index.aspx.

Right now i can do this with 2 regx rules, but was hope for 1 rule to handle both case (with or without the trailing slash). is there an advantage to 1 rule verses 2 rules.

any help would be great!

Thanks