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At a dinner last night, my friend Lan did a magic trick. Any ideas how it worked?

First, Lan took a number of cards out of a 52-card deck. I don't know exactly the number of card. To be sure that the cards are not prearranged, she gave me the cards and shuffled the set of cards by myself. After that she fanned cards and asked me to pick one card. I looked at them. I reput the card in any position in the deck of cards. I shuffled the set of cards by myself again and then gave them to her. She fanned cards, looked at them and picked the one that I chose. I don't really have any knowledge about card magic . So please forgive me if this is an obvious problem to you.

Here is the video showing the magic: https://streamable.com/zb5vp

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  • $\begingroup$ you told her what card you picked? $\endgroup$
    – JMP
    May 14, 2018 at 3:48
  • $\begingroup$ I am not sure what you are thinking. This is a magic so of course I will not tell her what the card I pick is. I just pick one card and then put it back again as in the video. $\endgroup$
    – emnha
    May 14, 2018 at 4:17
  • $\begingroup$ the audio stream is a bit weak, so you can't say that you didn't tell her the card $\endgroup$
    – JMP
    May 14, 2018 at 4:20
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    $\begingroup$ Not really sure what you mean. The video is my friend with me. So of course I know that I didn't tell her the card. Also the language is not English so it doesn't help much. $\endgroup$
    – emnha
    May 14, 2018 at 4:27

3 Answers 3

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If cards are not prearranged then it is impossible to do this trick.

It is so simple arrangement that you wouldn't notice.

The arrangement is that those cards does not contain any diamonds and any even numbered cards of others too. And they are all in same order. Not rotated 180 degrees.

Because

In a deck there are only diamonds and any even numbered cards which will be seen same by rotating cards 180 degree. So to do this trick they must be excluded.

Lan got your card by

As there was no diamonds and any even numbered cards and all the cards were in same order, she just rotated the whole deck by 180 degrees when you weren't seeing at the deck after picking up the card.

This way

When you place your card in the deck regardless of any place, only your picked card would be rotated 180 degrees than the rest.

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  • $\begingroup$ Aha, I've got it. Other people also have the same answer but you explained it in more detail. Thanks. $\endgroup$
    – emnha
    May 14, 2018 at 7:06
  • $\begingroup$ Welcome @anhnha. You may accept my answer as solution if you like it. $\endgroup$
    – prit.patel
    May 14, 2018 at 7:44
  • $\begingroup$ It is fairly risky to do this trick with people who know playing cards. That deck was clearly not a 52 card deck. $\endgroup$
    – Ian
    May 14, 2018 at 8:24
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    $\begingroup$ It is risky to do any card trick with peoples who knows about cards. And of course the deck was not of 52 cards because anhnha said that to be precise "Lan took a number of cards out of a 52-card deck. I don't know exactly the number of card." So the trick can be done if the deck is arranged in a manner that all the excluded cards are on bottom so we can take the cards above them which will be on top. So nobody will notice anything. @Ian $\endgroup$
    – prit.patel
    May 14, 2018 at 8:46
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    $\begingroup$ Ha. I'd have accidentally broken this trick by the way I shuffle - I end up with half the deck rotated each time I shuffle! $\endgroup$
    – AndyT
    May 14, 2018 at 13:38
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She knows your card because

All cards were in the same direction, and she flipped the deck after you took one card (exactly when you showed it to the camera). So in order to find your card, she checked one by one the cards to find the reversed one.

The key moment is at

0:45, you can catch her flipping all the cards.

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  • $\begingroup$ Thank you. I also thought about this possibility but as you can see from the video (the ending part) it is almost clear that the picked card is not reversed one comprared to the rest. $\endgroup$
    – emnha
    May 14, 2018 at 6:55
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    $\begingroup$ It is. Actually the card is reversed compared to the others, but because she flipped the deck all cards are pointing down, the only one pointing up is yours. $\endgroup$
    – Saeïdryl
    May 14, 2018 at 6:57
  • $\begingroup$ But whether one card is pointing up or down it is till exactly the same? $\endgroup$
    – emnha
    May 14, 2018 at 7:02
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    $\begingroup$ Look at this picture imgur.com/a/NqJB4yT Jaap was more precise, odd values of hearts, spades and clubs all have a central sign that is different if reversed. $\endgroup$
    – Saeïdryl
    May 14, 2018 at 7:07
  • $\begingroup$ @Saeïdryl: On many decks the sixes of hearts, clubs, and spaces, and the seven of diamonds is non symmetric. Sometimes the six of diamonds and non-diamond eights are non-symmetric as well, It might also be possible to use all cards backs is not perfectly symmetric (even if the design is symmetric, the printing will often not be perfectly centered). To make things less obvious, one could arrange the deck so that a known subset of cards are upside-down, though this would be easiest if one didn't need to look at the backs of the cards. $\endgroup$
    – supercat
    May 14, 2018 at 19:21
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Note that

it is no a full deck, and all the cards have odd values, and do not include any diamonds.

This allows her to

see when a card is upside down by the direction of the centre pip. She turned around the deck before you put the card back, making your card upside down compared to the rest.

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  • $\begingroup$ Thanks. I also thought about this possibility but as you can see from the video (the ending part) it is almost clear that the picked card is not reversed one comprared to the rest. $\endgroup$
    – emnha
    May 14, 2018 at 6:54

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