Grab & GuessDiscrete Mathematics Level 2
You friend challenges you to play "Grab & Guess" game. As the name suggests, he will grab a handful amount of coins from his money bag, and you'll guess whether the number of coins is odd or even.
Each correct guess will grant you 1 dollar before your friend puts the coins back and resumes the game, and you can continue playing infinitely as long as it's the right guess. On the other hand, the wrong guess will end the game immediately.
If your friend charges you 1 dollar as an entry fee, will this game earn or lose you money? (Assume there's no cheating!)