Since $$50\div(3+2)=10$$ which has no remainder, the $$50^{\text{th}}$$ colored lantern is yellow. 
A series of colored lanterns are arranged in the pattern: red, red, red, yellow, yellow, red, red, red, yellow, yellow $\cdots$ The $$50$$\textsuperscript{th} lantern is~\uline{~~~~~~~~~~}~. 
[a] red 
[b] yellow 