1/5×1/6×1/7+1/6+1/7+1/8+1/6×1/7×1/8=733/1680
过程:1/5×1/6×1/7+1/6+1/7+1/8+1/6×1/7×1/8
=1/6×1/7(1/5+1/8)+1/6+1/7+1/8
=1/42×3/40+13/42+5/40
=733/1680
1/5×1/6×1/7+1/6+1/7+1/8+1/6×1/7×1/8
=1/1680
1/5×1/6×1/7+1/6+1/7+1/8+1/6×1/7×1/8
=1/6(1+1/5×1/7)+1/7+1/8(1+1/6×1/7)
=1/6(1+1/35)+1/7+1/8(1+1/42)
=1/6×36/35+1/7+1/8×43/42
=6/35+1/7+1/8×1/7×43/6
=1/7×6/5+1/7+1/8×1/7×43/6
=1/7(6/5+1+43/48)
=1/7×(11×48+5×43)/240
=743/1680
1/1680