amount of dry yeast for 10 gallons

have never used dry yeast before... how many packages of dry yeast for 10 gallons?

What is the expected OG of the brew? For a typical APA or something I would use 2. For high gravity stuff like a tripel, RIS, etc I would use 3.

Also you might check out the Mr Malty Pitching Rate Calculator.

I tend to split one packet between two 5 gallon pails.

Apparently Pro brewing operations pitch way more yeast than home brewers. Mr. Malty as posted above is a much better reference than most chatter. You want your yeast to take off quickly with the least amount of stress producing off flavors and you want them to overwhelm any other organisms trying to take hold of your wort. If you go to the Doctor because you have a serious infection you don't ask for half doses of antibiotics to save a few bucks.