Let $X_{1}$, $X_{2}$, $X_{3}$, $X_{4}$, $X_{5}$ and $X_{6}$ be real-valued random variables that have the same probability distribution with finite moments, and they are independent. Does anyone know how to apply Markov inequality to show that $$ P\left(X_{1}+X_{2}+X_{3}+X_{4}+X_{5}+X_{6}\le3\right)\le2P\left(X_{1}\le1\right)? $$
Thanks for any helpful answers!