Hi

I would really appreciate some help if possible. I would like to know a formula I can use to solve the following problem:

Database of 100 items

Products are a collection of 20 items from the database.

Each product must not contain more than 50% of the same items as any other product. (Order of items within the product is not relevant).

How many products can I create from the database of 100 items. And what formula can I use should the number of items in the database be variable, or the number of items required by any product be variable. (For example a database of 60 items, where products are a collection of 9 items - or any other combination).

I hope that makes sense, please do let me know if I've not been clear enough though.

Many thanks in advance.

Chris