Welson's stuffed sandwich
In the student cafeteria, there are 2 types of bread, 3 kinds of stuffing and 5 types of spices. For the preparation of a sandwich, John uses 1 type of bread, 1 kind of stuffing and 2 different types of spices. If John eats 7 sandwiches per week, how many weeks will it take such that John must eat a sandwich which he has already eaten?
This problem is posed by Welson G.