[lek2554]

$\binom{27}{27} +\binom{28}{27}+\binom{29}{27}+...+\binom{50}{27}=\binom{28}{28} +\binom{28}{27}+\binom{29}{27}+...+\binom{50}{27}$

$\binom{n}{r} +\binom{n}{r-1}=\binom{n+1}{r}$