\(\dfrac{1}{2.3}+\dfrac{1}{3.4}+\dfrac{1}{4.5}+\dfrac{1}{5.6}=\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}=\dfrac{1}{2}-\dfrac{1}{6}=\dfrac{4}{12}=\dfrac{1}{3}\)
1: 2x3 + 1:3x4 + 1: 4x5 + 1:5x6
=1: 6 + 1: 20 + 1:30
= 1 : ( 6 + 20 + 30 )
= 1 : 56
= 1/56