2/3×4/5 3/4:6/8 5/9-2/7 2/5+3/8
2/3•4/5=8/15 3/4:6/8=2/2=1 5/9-2/7=17/63 2/5+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