А)30/3+9/3=10+3=13
40/4+8/4=10+2=12
60/3+3/3=20+1=21
80/2+4/2=40+2=42
б)40/4+36/4=10+9=19
50/5+45/5=10+9=19
70/7+42/7=10+6=16
80/8+56/8=10+7=17
в)64/8+32/8=8+4=12
54/9+72/9=6+8=14
35/7+49/7=5+7=12
42/6+48/6=7+8=15
г)120/4+24/4=30+6=36
180/6+36/6=30+6=36
350/7+49/7=50+7=57
360/9+63/9=40+7=47
Да, правильно. 10 + 2 = 12
1. (27/28-5/9)-(-(1/28)+(8+4/9))=-8
1. 27/28-5/9=243/252-140/252=103/252
2. -(1/28)+(8+4/9)=-(9/252)+(8+112/252)=8+103/252
3. 103/252-(8+103/252)=-8
2. -(-(20/27)+3/8)+(-(5+5/8)+(4+7/27))=-1
1. -(20/27)+3/8=-(160/216)+81/216=-(79/216)
2. -(5+5/8)+(4+7/27)=-(5+135/216)+(4+56/216)=-(1+79/216)
3. -(-(79/216))+(-(1+79/216))=79/216-(1+79/216)=-1
698,5:0,5=1397
698,5:0,1=6985
698,5:0,01=69850