card help: There’s this mind-reading card trick and I can’t figure out how to do it! - Help.com

Here’s a link to a very similar trick that uses the same principles.

http://mathematics.hellam.net/maths20…

The card is determined by elimination. The questions asked are designed to maximize what the magician learns at each step. Follow the link above and walk through the trick. Look carefully at where the cards from the row you pick the first time show up on the second round — they are evenly distributed with three of the nine cards in each of the three rows. This means that after two rounds, they have narrowed it down to three cards. On the third round each of those three cards is in a different row, so whichever row you pick tells them the card.

Does this make the trick you are asking about easier to understand?

Do you understand the trick shown at that web site, but you don’t see the relationship, or does the card trick shown at that site not make sense to you either?

Asking you if the famous scientist you are thinking of is on each of the other cards is similar to asking you which row the card is in. If you say “Yes, it’s on this card”, then they just need to find another card that shows only half of the scientists on the first card. Depending on whether you say that the person you are thinking of is on that card, they narrow it down to either the half shown on that card or the half not shown on that card. If the cards are designed carefully ahead of time they could even show you all the cards at once, and the answers would tell them who you are thinking of. For example, maybe Madame Curie is the only person on all the cards, while Albert Einstein is only on cards 1 and 3, and so on with a different combination for each card.

Well, maybe it’s magic.