Rezolvare :
a) 31+205-5+4+27-26=
=236-5+4+27-26
=231+4+27-26
=235+27-26
=262-26
=236
b){7+7×[7+3 ×(5+15-15)]}-161=
={7+7 ×[7+3 ×(20-15)]}-161
=[7+7 ×(7+3×5)]-161
=[7+7 ×(7+15)]-161
=(7+7×22)-161
=(7+154)-161
=161-161
=0
c) 10×{2+10×[126+10×(24+12-6)]}-42600=
=10×{2+10×[126+10×(36-6)]}-42600
=10×[2+10×(126+10×30)]-42600
=10×[2+10×(126+300)]-42600
=10×(2+10×426)-42600
=10×(2+4260)-42600
=10×4262-42600
=42620-42600
=20