375+178+21+125+74=(375+125)+(178+22)-1+74=500+200-1+74=773
375+178+21+125+74=375+125+178+21+73+1=500+200+73=773
=(375+125)+(178+21)+74=500+199+74=500+200+74-1=773
=(375+125)+(178+22-1)+74=500+200-1+74=773