3 - + 0,8= 7 2 - × 0,5= 9

3/7 +0.8 =3/7. +8/10 =3/7 +4/5 =(3*5 +4*7) /35 =43/35 =1 целая 8/35 2/9 *0.5 =2/9 *1/2 =2/(9*2) =1/9