Can you please tell me how to bake potatoes for a group of 40 people?

You will need to wash the potatoes then prick the surface with a fork. Place them one level deep in a pan or put them directly on the oven rack and cook for about one hour to 1 hour 15 minutes at 400°F (the potato is fully cooked when the internal temperature reaches 210°F). Here’s a suggestion for keeping them warm: put hot water in a cooler then drain the water and add the cooked potatoes.  Seal the top.  This will help keep warm for about 30 minutes.