\(\dfrac{1}{1x2}+\dfrac{1}{2x3}+\dfrac{1}{3x4}+...+\dfrac{1}{49x50}\)< 1
= (\(\dfrac{1}{1}-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+...+\dfrac{1}{49}-\dfrac{1}{50}\))
= \(\dfrac{1}{1}-\dfrac{1}{50}\)
=\(\dfrac{49}{50}\)
\(\Rightarrow\dfrac{49}{50}< 1\)