Mathematical Magic Show

Numbers trick

Worksheet - Binary 1-15 magic trick.pdf

Cut out the 4 cards and then get the person to choose a number between 1 and 15.  Then ask the person if their number appears on each card.  Add up the numbers in the top left hand corner of each card and that has their number on it.  E.g. if their number was 7 then it appears on the 1,2 and 4 card but not on the 8 card so the number is 1+2+4=7.  Children like this trick a lot and will play it on their friends and family at home.

Hole in a piece of paper.

Challenge the class: Can you make a hole in a piece of paper big enough for a person to fit through- or a whole class to fit through?

  Here is the pattern you need to copy to cut out the hole. 

1) Fold the paper in half length ways so you get a long strip with the lines on the outside. 
2) Then cut the vertical lines out, some will orginate from the folded edge and the alternate ones will originate form the open edge. 

Now we have to cut down the middle:
3) Reform the paper into the original long strip,
4) Gently tease open the paper to make an A4 shape again. 
5) Then cut down the middle (make sure you don't cut the endmost strips).

To make the hole bigger either make the lines longer (but not so that they cut through the whole paper) or have a narrower gap between each section.  Our record is 18 people in the hole including one pupil with a wheel chair.

Moebius Strip

Fold a strip of paper to form a ring, explain that this has 2 sides, an inside and outside.  Can you make a shape which has only one side?

Prove that it has only one side, by drawing a line all the way around the middle.

Extension when you cut a ring down the middle 2 halves are formed,what happens when you cut a Moebius strip down the middle?

Answer one ring with a twist in it.

  What happens when you cut this ring in half. 

2 rings appear joined together.

2 paper clips.

This trick used to be done on a £1 note being the right strength of paper, however any paper in a similar dimensions will work.   The paper clips should fly out joined together when the two ends are pulled.

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Optical illusion

This illusion is based on a triangle made of 4 pieces.  One way of fitting them together produces a right angled triangle.  Another way produces a right angled triangle with a hole in it, however the two triangles look the same size.  How does this work?

http://www.moe.edu.sg/maths/jul99/HowCan.htm

 The trick is that the slope of the triangle is not quite straight, one way the slope bulges outwards towards the middle thereby making the triangle smaller and fatter,  the second way the slope collapses inward thereby making the triangle longer and thinner thereby making the hole appear.

Maths and magic websites

http://plus.maths.org/issue14/features/eastaway/

http://www.easymaths.com/Curious_Maths_magic.htm

http://perso.wanadoo.fr/therese.eveilleau/pages/usa_accueilF.htm