(4/9+6/7+5/21)÷(2/9+3/7+5/42)
=(2/9×2+3/7×2+5/42×2)÷(2/9+3/7+5/42)
=2×(2/9+3/7+5/42)÷(2/9+3/7+5/42)
=2×[(2/9+3/7+5/42)÷(2/9+3/7+5/42)]
=2×1
=2
(4/9+6/7+5/21)÷(2/9+3/7+5/42)
=(2/9×2+3/7×2+5/42×2)÷(2/9+3/7+5/42)
=2×(2/9+3/7+5/42)÷(2/9+3/7+5/42)
=2×[(2/9+3/7+5/42)÷(2/9+3/7+5/42)]
=2×1
=2