The game "Spot It!" consists of a deck of cards.
In the original version of the game, every card has 8 symbols on it. If you pick any two cards, exactly one symbol will be the same on the cards.
In the kids version of the game, every card has 6 symbols instead, but you still have exactly one match of symbols if you pick any two cards.
Assume that the deck contains the same number of every symbol (that is, no symbol is more common than another).
In a deck with N symbols per card:
a) How many cards will there be at most?
b) How many symbols will there be?
(See also https://brilliant.org/discussions/thread/spot-it-problem-version-2/)