I don’t remember an Abbott and Costello routine on the missing dollar, but do remember fondly the many times they showed that 7*13=28 by screwing with positional notation. I play this for any class I teach where positional notation or base conversion is a thing, so mostly numerical methods or math history classes. https://www.youtube.com/watch?v=xkbQDEXJy2k Steve On Sep 5, 2020, at 2:08 PM, James Propp <jamespropp@gmail.com<mailto:jamespropp@gmail.com>> wrote: Is there a mathematical grift along the lines of the missing dollar riddle?: https://urldefense.proofpoint.com/v2/url?u=https-3A__en.wikipedia.org_wiki_M... I get the feeling I’ve seen such a thing in a movie, or maybe an Abbot and Costello routine. I thought I might find what I’m looking for in “Paper Moon”, but I could only find a clip showing a two-person con involving a marked $20 bill. Jim Propp _______________________________________________ math-fun mailing list math-fun@mailman.xmission.com<mailto:math-fun@mailman.xmission.com> https://urldefense.proofpoint.com/v2/url?u=https-3A__mailman.xmission.com_cg...