This trick appears to be mathematical but perhaps it is not!
Can you change this square into two using only a pencil? You are not allowed to come anywhere near the screen (or whiteboard).
The Trick: Carefully use the blunt end of a pencil to push up the lower eye lid of one eye and you will see double!
Each student is asked to think of a number between 2 and 9 inclusive (or ace, jack, queen or king). Whatever number they have chosen, there are four cards in their pack with that value. Students are asked to shuffle the pack while thinking about their cards.
Students are considered to have magical powers if two of their cards come
together in the pack (well there might be one card between them but for the
purposes of this exercise we will call that coming together).
Most students should find that this works for them ... so they have magic powers ... or have they?
The Trick: In fact this is an example where the odds are weighted in favour of a success ... can you estimate the probability from the results of this activity?
"There aren't many grey elephants living in Denmark are there?"
Virtually everyone in the room will have thought of Denmark as their country and as elephant as their animal. Is this magic?
Students can now investigate the probability of this happening. Having first satisfied themselves that everyone will arrive at the letter D independently of their starting number, how many countries are there starting with D?
How many animals beginning with E? Of all the animals beginning with E how likely is a person to choose elephant? Perhaps a survey might answer this question.
Students could now be asked to make up for themselves a similar trick (but not using Elephants from Denmark). Try out the tricks on some other students and teachers.
Finally a demonstration of tree diagrams can be used to explain the probabilities of these tricks working.
Update November 2014: The 96% and 85% on the tree diagram above were made-up figures for illustrative purposes only. We have now conducted our own survey to see what those figures should be. You can see the results on the Predictive Survey Results page.]
You can amaze your students by pretending to add up a whole column of
three digit numbers in a couple of seconds.
Ask three students to write three digits each on a piece of paper as if they are to be added and return the paper to you.
You write two more numbers below those. Choose your first number (which is the fourth one in the problem) so that the first number and fourth numbers add up to 999. Choose your next number so that it adds with the second number to give 999.
Give a student the paper and ask them to add up the numbers on a
calculator. Then the student could return the paper to you. Look at it
briefly as if you are adding the numbers in your head and announce the
The answer will be 2000 plus the third number minus 2 which you could compute very quickly once the student returns the paper.
This could be followed by a class discussion about how this trick works ... students practise with friends.
The Teacher writes a number on a large piece of paper. The students can
see this going on but can't see which number it is. The paper is the put in
an envelope or a box and put in a safe place in view of the students.
The Teacher then asks a student to think of a very large number. This number is written on the board in words.
"How many letters are in these words?" ... the answer is written underneath in words...."How many letters are in these words?" ... and so on repeating the process again and again till the list of numbers has reached the bottom of the board. The envelope is then opened to reveal the number FOUR which will be the last number written on the board.
F O U R
"What if we start with a different number?" ... another student
volunteers a different starting number which eventually generates four
"Does this always happen?".. students try some of their own.
"Why does it always happen?"
"What about other languages?"
Students now do an investigation looking at the properties of the number words in different languages. They can use foreign language dictionaries or the internet as appropriate. They should produce a write up of their findings for their folders.
many calculations have short cuts or tricks associated with them which enable students to perform the calculations quickly in their heads.
A list of such tricks can be found here.
Here are a couple of examples:
Did you know that there is a quick way of squaring a two digit number which ends in 5?
Just multiply the first digit by that number plus one.... stick a 25 after your product and there's your answer .... simple ?
Q. What is 35 squared?
.....now stick on the 25
...........the answer is 1225
Do you know why it works?
The eleven times table has always been very easy to learn up to 9 x 11. Here's a way of multiplying large numbers by 11 too:
Q. What is 324 x 11 ?
A. Write down the first digit ... 3
.......Add the first and second digits ... 3 + 2 = 5
.......Add the second and third digits .. 2 + 4 = 6
.......Write down the last digit ........... 4
The answer is 3564.
Try it yourself ... multiply 543 by 11
Do you know why it works?
Does it work for all three digit numbers?
A large house plan made from 9 pieces of carpet (each 3m by 3m) is set out in the middle of a large room as shown:
A student is dressed to look like the murderer(!) and stands on the
carpet piece marked "Hall".
A teacher (acting as Sherlock Holmes) explains that the murderer will be tracked down in the house and arrested. Sherlock is blindfolded.
A second student throws the dice and states the number on the dice out loud. The murderer walks through that many doors on the plan of the house.
Sherlock says "I know the murderer is not in the kitchen (or name of other room) , so will someone please take away the kitchen"
A third student takes away the piece of carpet labelled "kitchen". the murder from now on cannot step on the area which was once the kitchen.
The process is repeated a number of times until Sherlock can say "I know that the murderer is in the ........... (name of room), you are under arrest.
"How does the trick work?"
Well if the murderer starts in the hall, four rooms are one door away (study, bathroom, dining room and conservatory). We shall call these rooms odd rooms.
The other rooms are two doors away. We'll call these rooms even rooms.
If the number on the dice is even, Sherlock knows that the murderer must have walked into an even room so can ask for one of the odd rooms to be removed.
The process continues. Sherlock uses the principles that:
Odd + odd = even
Even + even = even
Even + odd = odd
Odd + even = odd
... to keep track of the rooms the murderer can't be in. By process of elimination the correct room can be found (In practice Sherlock must reserve the right not to remove a room in certain cases)
This could be followed by whole group discussion about how the trick was performed (using student's own theories and words.
Students in pairs try to perform the trick using the a diagram and a counter to represent the murderer.
Acting as Sherlock requires a great mental effort keeping track of the rooms.
A number of items can be memorised in order by associating each item with
a place on a familiar journey.
For example 20 geometric shapes could be visualised at various places on the journey from bed to school each morning. The shapes could be visualised at places such as the bathroom, kitchen bus stop etc.
Students challenge each other to memorise the order and names of 20 shapes such as pyramid, sphere, octagon etc.
One technique for remembering a list of items in order is by associating each item with an item from the following children's rhyme:
One is bun
Two is shoe
Three is tree
Four is door
Five is hive
Six is sticks
Seven is heaven
Eight is gate
Nine is line
Ten is pen etc.
This activity could start by collecting from the students a list of ten
popular video films. Students are then asked to conjure up in their minds a
crazy image of the item from the list above involved in the action of the
Eg if the fifth film is The Sound of Music; a student might picture Julie Andrews being chased over the Austrian Mountains by a swarm of angry bees.
Working in pairs students could practice this technique by memorising ten items from a shopping list
Many mind reading tricks involve a "plant" in the audience secretly giving information to the mind reader. The way this information is given often involves mathematical codes or systems.
Nine objects are arranged in a 3 by 3 grid formation
While the magician isn't looking, the students are asked to choose an
object an concentrate on it. The magician can quickly identify the chosen
object by feeling the thought vibrations coming from it ... well not really.
One of the students has previously been asked to act as the "plant" giving
the magician a secret sign. Students are asked to work out some secret signs
which could correctly identify one of the nine objects.
One system could be that the plant and the magician agree to define each object in terms of its row and column (like a matrix). The plant uses the position of their head to indicate the row and arms to indicate the column.
Students are encouraged to invent similar (more complex) illusions.
(alternatively this trick could be performed using nine buckets placed upside down on the floor with an item being put under one while the magician isn't looking.)
"Black Magic" is a well known old party trick
in which a person apparently mind reads to find an object previously
selected by an audience. An accomplice helps by pointing to various objects
asking "is this it?". The mind reader always says no till after the
accomplice has pointed to a black object; the next object to be pointed out
will be the chosen object.
Students could devise similar mind reading tricks using number codes of other systems.
One person thinks of a number 1 - 20. They are asked which cards contain their number. The magician can work out the number by adding up the top left numbers on each of the selected cards.
How does it work? The numbers in the top left of each card are powers of two and any number can be expressed as a combination of powers of two. this can be shown to be the basis of the binary system.
This trick could be described by a teacher without showing the students a set of cards. Students challenged to make their own set of cards and extend for numbers greater than 20 (the trick works better the more numbers there are on each card). Students should practice performing this trick on each other using their own set of cards
Here's a more detailed Interactive version
The Online Psychic
Wouldn't it be impressive if you could instantly write down a 4x4 magic
square giving any total that a friend suggests. It can be done ... there's a
trick to it!
First you have to memorise the basic 4x4 magic square which gives a total of 34. (Memorising this could lead to some interesting multisensory work!)
Let's suppose your friend chooses the number 57. Firstly subtract 33 from
this giving 24.
Now replace the numbers 1, 2, 3 and 4 in the basic square with 24, 25, 26 and 27 in that order.
You now have a magic square with 57 as the sum of each column, each row, each diagonal and each 2 by 2 square within the larger square.
Why does this work? Look at the positions of the numbers 1 - 4. How are they significant?
Try some of the other areas of the Transum Maths website:
Comment recorded on the 3 October 'Starter of the Day' page by Fiona Bray, Cams Hill School:
"This is an excellent website. We all often use the starters as the pupils come in the door and get settled as we take the register."
Comment recorded on the 12 July 'Starter of the Day' page by Miss J Key, Farlingaye High School, Suffolk:
"Thanks very much for this one. We developed it into a whole lesson and I borrowed some hats from the drama department to add to the fun!"
Comment recorded on the 3 October 'Starter of the Day' page by Mrs Johnstone, 7Je:
"I think this is a brilliant website as all the students enjoy doing the puzzles and it is a brilliant way to start a lesson."
Comment recorded on the 3 October 'Starter of the Day' page by S Mirza, Park High School, Colne:
"Very good starters, help pupils settle very well in maths classroom."
Comment recorded on the 17 June 'Starter of the Day' page by Mr Hall, Light Hall School, Solihull:
I love you website I use it every maths lesson I have with every year group! I don't know were I would turn to with out you!"
Comment recorded on the 18 September 'Starter of the Day' page by Mrs. Peacock, Downe House School and Kennet School:
"My year 8's absolutely loved the "Separated Twins" starter. I set it as an optional piece of work for my year 11's over a weekend and one girl came up with 3 independant solutions."
Comment recorded on the 23 September 'Starter of the Day' page by Judy, Chatsmore CHS:
"This triangle starter is excellent. I have used it with all of my ks3 and ks4 classes and they are all totally focused when counting the triangles."
Comment recorded on the 9 October 'Starter of the Day' page by Mr Jones, Wales:
"I think that having a starter of the day helps improve maths in general. My pupils say they love them!!!"
Comment recorded on the 10 September 'Starter of the Day' page by Carol, Sheffield PArk Academy:
"3 NQTs in the department, I'm new subject leader in this new academy - Starters R Great!! Lovely resource for stimulating learning and getting eveyone off to a good start. Thank you!!"
Comment recorded on the 1 February 'Starter of the Day' page by M Chant, Chase Lane School Harwich:
"My year five children look forward to their daily challenge and enjoy the problems as much as I do. A great resource - thanks a million."
Comment recorded on the 1 May 'Starter of the Day' page by Phil Anthony, Head of Maths, Stourport High School:
"What a brilliant website. We have just started to use the 'starter-of-the-day' in our yr9 lessons to try them out before we change from a high school to a secondary school in September 2007. This is one of the best resources on-line we have found. The kids and staff love it. Well done an thank you very much for making my maths lessons more interesting and fun."
Comment recorded on the 17 November 'Starter of the Day' page by Amy Thay, Coventry:
"Thank you so much for your wonderful site. I have so much material to use in class and inspire me to try something a little different more often. I am going to show my maths department your website and encourage them to use it too. How lovely that you have compiled such a great resource to help teachers and pupils.
Comment recorded on the 11 January 'Starter of the Day' page by S Johnson, The King John School:
"We recently had an afternoon on accelerated learning.This linked really well and prompted a discussion about learning styles and short term memory."
Comment recorded on the 19 November 'Starter of the Day' page by Lesley Sewell, Ysgol Aberconwy, Wales:
"A Maths colleague introduced me to your web site and I love to use it. The questions are so varied I can use them with all of my classes, I even let year 13 have a go at some of them. I like being able to access the whole month so I can use favourites with classes I see at different times of the week. Thanks."
Comment recorded on the 10 April 'Starter of the Day' page by Transum, :
"Sorry Mike, because some of the starters link to live data on the Internet there is no CD version. Thanks for your comments."
"This has saved me a lot of time over my summer holidays - thank you."
D. Boyce, Rohwell
Monday, August 26, 2013
"Thank you and blessings."
Sadhana Bhat, Mpsmkbh@gmail.com
Saturday, October 19, 2013
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