Sam completed 2/3 of Wednesday's crossword and 1/3 of Thursdays crossword. In total, what fraction of the crosswords did Sam finish?

Sam completed 2/3 of the one on Wednesday and 1/3 of the one on Thursday, so he has done 3 thirds of both.

now, a whole is 1, in this case for thirds that'd be 3/3 for a whole crossword, for two crosswords that'd be 3/3 + 3/3 or 6 thirds, and Sam has completed only 3 thirds of that, 3 thirds is half of 6 thirds.