How do I do a 301 redirect because of duplicate urls

I am currently trying to do a 301 redirect for all the pages of a site i am working on. The problem is that this url:

http://site.com/cash/ 
http://site.com/credit/

and

http://site.com/cash 
http://site.com/credit 

display the same pages

This will result in a number of duplicate URL issues and start splitting your PageRank of our SEO.

I was trying to do that on my site where all the seo points to the non-slash version

BTW I have about 90 pages that i have to change...any ideas on a good way of achieving this

How do i do a 301 redirect in the htaccess to do this on all my pages

Edit:

So to understand correctly. this will do the 301 redirect

# Remove the trailing slash
RewriteCond %{HTTP_HOST} ^(www.)?example\.com$ [NC]
Rew开发者_JAVA技巧riteRule ^(.+)/$ http://www.example.com/$1 [R=301,L]

But how does this exclude folder1

RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d

and would i put that in the same htaccess file or create another htaccess file in the folder1 directory

You can add the following to your .htaccess to remove the trailing slash

# Remove the trailing slash
RewriteCond %{HTTP_HOST} ^(www.)?example\.com$ [NC]
RewriteRule ^(.+)/$ http://www.example.com/$1 [R=301,L]

Update

You can then choose to also add www

RewriteCond %{HTTP_HOST} ^example.com$
RewriteRule (.*) http://www.example.com$1 [R=301]

or remove it

RewriteCond %{HTTP_HOST} ^www.example.com$ [NC]
RewriteRule ^(.*)$ http://example.com/$1 [R=301,L]

Rather than using a 301, you could just use a rel canonical link.

You could use <shudder> mod_rewrite instead, if it's for an Apache server... It's disasterously inefficient but probably the best option if what you're bothered about is SEO