How long does it take to cook a three pound prime rib roast?

Bake the 3lb roast for 17 minutes in the preheated 450 degree oven, then reduce heat (without opening the oven door) to 325 degrees & continue roasting for about 35 minutes or until the temp reads 130 degrees (for medium rare). Remove from oven and let rest for at least 7-10 minutes before slicing.