A twist on Musical Chairs... minus the chairs you dont need much for this game.
Rules: people must walk around the room, spread out, not in clumps. They listen to the music playing. The person holding the music player/ phone stops the music and calls out "groups of 4" or "groups of 7" and those people must make groups of the numbered called as fast as possible. The group of people who has less people than called out number is out, and the music starts playing again and again until the person playing music stops it again and yells "groups of 2" who ever can not fufill the number called is out.
This game is played pretty quickly and lots of fun.