Beef tenderloin yields approximately four servings per pound, so 5 pounds is appropriate for 20 people. For large groups, it is best to roast it whole.
Beef tenderloin is a strip of meat that comes from between the cow's ribs and backbone. It is not responsible for much movement, so it is a tender cut of meat. For a 5-pound tenderloin, the roast should be baked from 50 to 70 minutes, depending on the desired level of doneness. An internal temperature of 135 degrees Fahrenheit yields medium rare meat, while 150 degrees yields medium. For even cooking, the tapered end of the tenderloin should be either trimmed or folded under.