Wow any audience with this no fail ice cream trick. Based on simple mathematical principals which you can learn about here, but appearing to be nothing more than magic!
This trick can also be found in the book, Mathematical Card Magic: Fifty-Two New Effects, by Colm Mulcahy, with a foreword by Max Maven. (A.K. Peters/CRC Press, 380 pp., 128 illustrations, August, 2013)