A chess riddle you can use some time on if you're bored.
We have a 9x9 Chess board here to play on. All you have to do is place 24 queens on the board, 12 black and 12 white ones.
What is the hard part about this you might ask. None of the queens must be able to attack a queen of the opposite color.
Only one guy I've shared this with have been able to complete it, so good luck.