How long to cook a 2.5 lb roast beef?

I can't give you a specific cooking time for a 2.5 lb roast beef without knowing more information. Here's why:

* Cut of meat: Different cuts of beef cook at different rates. A tenderloin roast will cook much faster than a chuck roast.

* Desired doneness: Do you prefer your roast rare, medium-rare, medium, or well-done? Each level of doneness requires a different cooking time.

* Cooking method: Are you roasting in the oven, slow cooking, or using a different method? Each method has its own ideal cooking time.

To help you find the right cooking time, please tell me:

* What cut of beef is it?

* What level of doneness do you prefer?

* How are you planning to cook the roast?

Once you provide this information, I can give you a more accurate estimate of the cooking time.