Ответ:

1. (16,23 + (-1,7)) + 12,41 = 14,52 + 12,41 = 26,93;
2. 2 1/6 + (-2 1/4 + (-3 3/5)) = 2 1/6 + ((-2+(-3)) + (5/20+12/20)= 2 1/6 + (-5 17/20)= (2+(-5)) + (10/60 - 51/60) = -4 41/60;
3. (-18,83 + 11,4) + (-12,3 + 19,73)= - 7,43 + 7,43=0;