21/40×6/7×2/9;2/3×5/6×27/40

21/40×6/7=9/20 9/20×2/9=1/10 ---- 2/3×5/6=5/9 5/9×27/40=3/8

1) 21/40×6/7=21×6/40×7=18/40=9/20 9/20×2/9=9×2/20×9=1/10 2) 2/3×5/6=2×5/3×6=5/9 5/9×27/40=5×27/9×40=3/8 надеюсь я помогла♡