2:2 2/3 +1 4/5*3 1/3-2 5/6
2/1:8/3+9/5*10/3-2 5/6=2/1*3/8+6-2 5/6=3/4+6-2 5/6=6 3/4-2 5/6=4 9/12-10/12=3 21/12-10/12=3 11/12