9.1. There are seven cards on the table. In one move, it is allowed to flip any five cards. What is the minimum number of moves required to flip all the cards?
9.1. Answer. 3 moves.

Obviously, one move is not enough. After two moves, there will be at least three cards that have been flipped twice, which means these cards will be in their original position.

Let's provide an example of flipping all the cards in three moves. Number the cards from 1 to 7 and flip cards numbered $1,2,3,4,5$ on the first move, $-1,3,4,5,6$ on the second move, and $-1,3,4,5,7$ on the third move.