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Puzzle 6: Flipping Cards

There are 7 cards sitting face down on table top.  You want to turn them all face up in the smallest number of moves.  A "move" consists of turning over 3 cards at a time.  The cards don't have to be adjacent, but you must turn over three at a time.  How many moves are required?
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Extension:  What about adding 2 cards and flipping one extra card each move?  How many moves would it take to have all cards face up?  For example, if there are 9 cards, flip 4 at a time, how many moves would make all the cards facing up?  Can you see the pattern and prove it?