How to reduce a recipe
 

I have a recipe for sauerbraten that I really like. The men's group at church do a sauerbraten dinner almost every year. This year I missed the dinner. :( However, I do have the recipe that they use. The problem is it is for 150 people. How do I reduce the recipe so that the marinade comes out in the correct proportions? Is there a formula or method for doing this?