I am cooking two three-rib roasts at the same time. Each weighs 7 lbs. In estimating the cooking time per pound, should I use 7 lbs or 14 lbs?
Use 7 pounds! Going by 14 will overcook the two smaller roasts.
And use a meat thermometer to check for desired doneness, 5 degrees less than done, cover with foil and let it rest before slicing.