\(\dfrac{1}{1.4}+\dfrac{1}{4.2}+\dfrac{1}{2.8}+\dfrac{1}{8.4}+\dfrac{1}{4.16}+\dfrac{1}{16.8}\)
= \(\dfrac{1}{4}.\left(1+\dfrac{1}{2}+\dfrac{1}{4}+\dfrac{1}{8}+\dfrac{1}{16}+\dfrac{1}{32}\right)\)
= \(\dfrac{1}{4}.\left(\dfrac{3}{2}+\dfrac{3}{8}+\dfrac{3}{32}\right)\)
= \(\dfrac{1}{4}.\dfrac{3}{2}\left(1+\dfrac{1}{4}+\dfrac{1}{16}\right)\)
= \(\dfrac{1}{4}.\dfrac{3}{2}\left(\dfrac{16}{16}+\dfrac{4}{16}+\dfrac{1}{16}\right)\)
= \(\dfrac{3}{8}.\dfrac{21}{16}\)
= \(\dfrac{63}{128}\)