Anyone know how to answer/attempt this question?
There are $n \geq 2 $ sets each containing 10 elements each. Any 2 sets contain 1 element in common and each 2 elements are only in the same set once.
Prove all elements occur in the same number of distinct sets.
Clarified in the comments: "each 2 elements are only in the same set once" means that if we pick any two elements, they will be found together in the same set exactly once, although each element separately could occur in multiple sets.