Seven dwarfs are sitting at a round table. Each has a cup, and some cups contain milk. Each dwarf in turn pours all his milk into the other six cups, dividing it equally among them. After the seventh dwarf has done this, they find that each cup again contains its initial quantity of milk. How much milk does each cup contain, if there were 42 ounces of milk altogether?
A few other Math Olympiad Problems on the blog:
Math Olympiad Problems
Moscow Math Olympiad Problems
Math Olympiad Problem : Overlapping Coins
USA Maths Olympiad Problem - 200th Puzzle
Correct answer posted by Akshay Kumar in comments! Detailed solution posted by me.