+ на - будет - - на - будет +
1) (16,23+ (-1,7) ) + (-12,41) = (16,23-1,7)-12,41 = 14,53-12,41=2,12
2) 2 1/6 + ( (-2 1/4) + (-3 3/5))=13/6 + (-9/4-18/5) = 13/6+(-45/20-72/20)=13/6-117/20 = 130/60-351/60=-221/60= -3 41/60
3) (-18,83 + 11,4)+ (-12,3 + 19,73)=-7,43+7,43=0