2 Math Tricks To Impress Your Students With!

 If you look at various books and workshops, there is a move out there to create a hook to capture your student's interest.  Many of the suggest hooks are harder to implement in math but there are things you can do to capture their attention.

This is one popular trick from the 1990's that could be used in the class.  It is one magician David Copperfield has used as part of his magic act.

On 12 index cards, write the numbers one to twelve on them.  Arrange the cards in a circle so it resembles a clock face.

Have the students choose one number from the face of the clock. They then spell out the number beginning at 12 and moving clockwise.  For instance if they choose six, they would start at 12 and spell out s-i-x so they move through one to two and end at three.  Now you should be on the number 3.  You would spell out three so you'd move 5 spaces to the number 8.  Now you spell the eight beginning at the number 8 so you should end on the one because you keep going.

At this point you tell students that you do not know what number they are one but you know they are not on the 2, 4, 8, or 12.  Once those numbers are removed, have the students spell out the letters of the number they'd last landed on which in the case of the example is one.  They simply skip the spaces of the missing numbers.  So I spell out one and end up on the number 6.  At this point, you tell they they can't be on the 10, 3, 9, , 1 or any other number but the six.

No matter what number you select, if you follow this sequence, you will always end up on the 6 because it is based on the Kruskal count, named for mathematician Martin Kruskal.  The Kruskal count which is a special case of the absorbing Markov chain and is based on the idea of when the probabilities line up, people end up with the same number.  This site has a youtube video which shows the trick and then explains the math behind it.

Here is another math trick based on cards.  Make sure you have a full deck of 52 cards.  You can shuffle them or have someone else shuffle them.  Count out any 9 cards from throughout the deck.  You might want to count three groups of three out from the different parts of the deck.  Have the student select one of the 9 cards.  Place the card the student chose on the top of the 9 cards and you put the remaining cards on top of the students cards.  If you want you can get fancy with a couple of small fake cuts or you can move on to the next part.

Now you are going to make four piles but before you begin counting down from 10, you have to know that all jacks, queens, and kings are worth 10 while the ace is one.  So begin by turning the top card over and say 10, then the next card and say 9.  You continue doing this until the number of the card matches the number you just said.  When that happens, you stop and begin a second pile.  If you get all the way to one and none of the card values match the count down number, you place a card face down and go to the next pile.

When you get finished with the fourth pile, add the face values of top cards for all four stacks and that tells you what position the card the student chose is in.  If you have cards covering all four stacks so no values show, that last card on the 4th pile is the chosen card.  If you have trouble following my directions, check the video that explains it here.  So now you have at least two tricks you can use to start your class and grab student attention.  I hope to cover a few more later in the summer.  Have a great day and let me know what you think.