Five Will Get You Ten Meaning

(idiomatic) I strongly believe

Example: 1957, Clyde Brion Davis, Unholy Uproar
  Five will get you ten that he's either gone or dead by midnight Sunday.
2003, F. Winston Pate, Serenity
  As it is I'm going to be in big trouble financially if I lose my job and five will get you ten the bastards will try to drum me out.