Lose Your Marbles! can be played with several different board sizes.  For the 5 x 5 board, the best possible solution uses only 5 different marbles.  The 6 x 6 board can be solved with 7 different marbles, as well as the 7 x 7 board.  The 8 x 8 requires 9 different marbles.

Don’t feel discouraged if you can’t get the best solution right away.  Allow yourself one or two extra marbles, then see if you can trim down to the best solution.