А)28,345+311,63=339,975\339,975-311,63=28,345\339,975-28,345=311,63(б)108+12,34=120,34\120,34-108=12,34\120,34-12,34=108(в)2,31-0,45=1,86\1,86+0,45=2,31\2,31-1,86=0,45(г)8,4-1,265=7,135\7,135+1,265=8,4\8,4-7,135=1,265\(д)72-3,14=68,86\68,86+3,14=72\72-68,86=3,14\(е)2-0,002=1,998\1,998+0,002=2\2-1,998=0,002.