we turn coffee into puzzles

Mystery Sum Sudoku The numbers 1--9 must each appear exactly once in each row, column, and block. In addition, all shaded regions of a given color add to the same sum; for example, if one red shaded region has entries that sum to 21, then all red shaded regions in that puzzle sum to 21. The sums are not given; you must determine them yourself. Appeared in +Plus Magazine, part of the Millennium Mathematics Project based at Cambridge University, Issue 43, June 2007.