1/2×2/3×3/4×4/5×5/6
=(1×2×3×4×5)/(2×3×4×5×6)
=1/6
(1-1/2)×(1/2-1/3)×(1/3-1/4)×(1/4-1/5)×(1/5-1/6)=1×6/1=1/6