Răspuns:
423+(4x2)=423·4+423·2=1692+846=2538
(2x9)-(2x4)=18-8=10
(2x9)-(2x4)=2(9-4)=2·5=10
4x 70-4x50= 280-200=80
4x 70-4x50=4(70-50)=4·20=80
(100x7)+(20x7)=700+140=840
(100x7)+(20x7)=7(100+20)=7·120=840
(80x5)–(30x5)=400-150=250
(80x5)–(30x5)=5(80-30)=5·50=250