解：
原式
=1÷(2÷3)÷(3÷4)÷(4÷5)÷(5÷6)
=1÷2×3÷3×4÷4×5÷5×6
=1÷2×(3÷3)×(4÷4)×(5÷5)×6
=1÷2×6
=0.5×6
=3
1÷（2÷3）÷（3÷4）÷（5÷6）
=1÷2/3÷3/4÷5/6
=1×3/2×4/3×6/5
=1×12/5
=12/5
4/9÷[5/6-(1/6+1/3)]
=4/9÷[5/6-1/6-1/3]
=4/9÷[2/3-1/3]
=4/9÷1/3
=4/3
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