Add certain promo to products on magento - mix and match promotion

Hello. We need to set up a promo on our magento website on a range of 100 products. if user buys any of these 100 products and adds a quantity of 10 to the checkout then the buyer pays a fixed discount price. they can mix and match between these 100 products but the total product from this category must add up to 10 in order for them to get this discount. If you can do this via teamviewer only. and you will be awarded after completed.