Question: how long do you cook a 3.5 lb beef roast?
Answer: Insert a meat thermometer into the thickest part of the roast going about half way through the roast. You want the bottom of the thermometer to be in the center of the roast. Cook for 20 minutes a pound. A 3.5 lb roast takes about 1 hour and 15 minutes for a rare roast, but watch the thermometer reading.