4/5*5/7=4/7; 8/9*3/5=8/15; 9/2*2/9=1; 8/21*7/10=4/15; 8/15*25/28=10/21
3/7*2=6/7; 3*1/6=1/2; 9*5/6=7 целых 1/2; 2/5*15=6; 1/4*4=1; 5*1/5=1;
2 1/3*2=7/3*2/1=14/3=4 2/3
4*1 1/2=4/1*3/2=12/2=6
1 1/3*9=4/3*9/1=12
3/7*2 1/3 =3/7*7/3=1
1 1/3*1 1/2=4/3*3/2=2