I remember marking a big red checkmark next to this item in one of my first EZ Magic catalogs, back in about 1974. (A checkmark meant I had to have that trick, if I was ever going to be the World's Greatest Magician). I just pulled out one of my oldest surviving EZ Magic catalogs ( #30, from 1980), and looked at that catalog description again. I probably was sold on it by the catalog description, that included the words "practically works itself" and "does not require any adding". (Both generally true statements). I'm sure the sentence "you immediately know the thought of number" also piqued my interest. (not exactly a true statement, unless you define "immediately" as "after the spectator tells you which row their number is in on three different cards".)
Of course, the main reason I had to have this trick is that the illustration featured a bearded magician wearing a turban which I thought was very cool. :-)
But it seems that sometime in the 1980's, EZ Magic (D Robbins Company) stopped making Mysti-Math. And over the last 3+ decades, the trick has become harder to find than a bearded magician in a turban.
Despite my avid desire to own this trick back in my early magic years, I never did buy one. And in my 40+ years in magic, I had never actually seen a Mysti-Math, until recently when I came across a couple of nice examples. I kept one for myself (at last!) and offer the other to some lucky vintage magic collector.
MYSTI-MATH is smaller than I expected it to be (since old magic catalogs always made props seem bigger and better than they really were...), but it is a good size for close-up performance. The cards are about 4 inches square. It is simple to do, and more of a puzzle than a mystery, in my opinion, but for those who like mathematical oddities, it is a pretty cool prop that will intrigue an audience of math geeks (like me).
The spectator thinks of any number on the "Control Card" (they range from 1-64). You then hand her card #1, which has a big square hole in it, and four rows of printed numbers. You ask the spectator which row her thought-of number is in, and after she tells you the row (not the number), you place card #1 onto the control card. You show here cards #2 and #3, which also have four rows of numbers, and four narrow slots cut out in them. After she tells you the row her number is in on each card, you set them down on the pile with the Control Card. When the four cards are squared up, the thought-of number is revealed in the aligned slots.
The cards are printed on stiff but thin cardboard, pre-perforated around the necessary slots and hole. I am guessing that most Mysti-Math's were ruined by young magicians who bent and tore the cardboard while trying to push out the perforated slots and holes. Maybe this is why they are so hard to find in any condition now -- they all got torn, bent and tossed away.
The one in the photo is from my own collection, and I have opened the slots. The one for sale here is still intact as issued by EZ Magic. (If you want me to carefully open the slots before I send it to you, I am happy to do so for you. Not difficult if you are careful and patient.)
Instructions sheet is included -- it references a copyright of 1950, when Mysti-Math was first introduced, but this prop and instruction sheet is likely from the early 1980s. But in unused condition.