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Calculati, folosind proprietatile adunarii: a) 75+138+25 b) 4+90+106 c) 197 +2457 +3 d) 23+78+27+22 e) 11+12+13+14+15+16+17+18+19.

Răspuns :

(75+25)+138=238
(106+4)+90=200
(197+3)+2457=2657
(23+77)+(78+22)=100+100=200
(11+19)+(12+18)+(13+17)+(14+16)+15=4*30+15=120+15=135