How to get a legendary card in clash royale?

Tapas Chawla, Playing Clash Royale since the release and follow it anywhere I can. To get a legendary card through chests is a matter of luck . Every chest has some probability of having a legendary card. If in Arena 7 you open your chests everyday you are likely to get a legendary every 54 days. 

BUT THE TYPES OF QUESTIONS YOU ASK ARE NOT RELATED TO STUDY