i saw on another question it said 1 pound feeds about 4 people assuming the pasta is the main course. so for 30 people, to be safe, i would buy/use 8 pounds of pasta. maybe 7 if you know some people...
Depends on what you are serving. A quarter pound hamburger would mean that it would serve four. If you put it into a spaghetti sauce, you can serve up a six or eight easily enough.