1целая2 / 5 × 2целых5 / 7-1целая2 / 5 × 3 / 14
5 класс Атамура

1 2/5*2 5/7-1 2/5*3/14=1 2/5*(2 5/7-3/14)=1 2/5*(2 10/14-3/14)==1 2/5*2 7/14=1 2/5*2 1/2=7/5*5/2=35/10=3,5

1 2/5×2 5/7-1 2/5×3/14==1 2/5(2 5/7-3/14)==7/5×2 7/14=7/5×2 1/2==7/5×5/2=7/2=3 1/2.