Four Grids, One Method
Solve the four grids in order: on the first, list the combinations of each clue on the side; on the second, try doing it in your head; by the fourth, the common sums, 3, 4, 16 and 17 in two cells, will come by themselves.
Four Grids for a Classroom
A sheet of four grids suits a classroom or a puzzle club: everyone gets the same sheet, and solvers who finish a grid move on to the next one. The grids are small but still printed large enough to write in comfortably.
Choosing a Level
Easy sheets are a gentle start for teenagers practicing mental addition. Medium and Hard sheets keep the same small size but ask for real deductions, which makes them a compact training ground before the larger single grids.