2/3×4/5
3/4:6/8
5/9-2/7
2/5+3/8

2/3•4/5=8/153/4:6/8=2/2=15/9-2/7=17/632/5+3/8=31/40

1) ⅔×4/5=8/15; 2) 3/4:6/8=3/4:8/6=2/2=1; 3) 5/9-2/7= 35/63-18/63=17/63; 4) 2/5+3/8=16/40+15/40=31/40