<span>20 - 18,6 : (6 11/15 - 4 3/20) =12,8,
1) </span>6 11/15 - 4 3/20= (6 - 4)+ (11/15 - 3/20)= 2 + (44/60 - 9/60) = 2+7/12= 2 7/12,
2) 18,6 : 2 7/12 = 186/10 : 31/12 = 186/10 * 12/31 = 36/5 = 7 1/5 (или 7,2),
3) 20 - 7,2 = 12,8
458:3 =458/3=(458+2)/3 =456/3 +2/3 =152+2/3 =152 (ост2) проверим 2+152*3=2+456= 458 458=458 673:4 =673/4 =(672+2)/4 =672/4 +1/4 =168+1/4 =168 (ост1) проверим 1+168*4 = 1 +672 = 673 673=673 489:9 = 489/9=(486+3)/9=486/9+3/9=54+3/9=54 (ост3) проверим 3+54*9 =3 +486 = 489 489=489