Here are four ‘tricks’ to amaze your friends.
But the really clever trick is explaining to them why these ‘tricks’ are mathematical and not magic. Like all good magicians, you should practise by trying them. Can you explain how they work?
This trick will impress even your maths teacher.
1. Magic Maths Trick
Think of a number.
Double it.
Add 10.
Halve it.
Take away your original number.
Is your answer 5?
Try this with a different starting number. Did you get a different result? Why does this happen?
Write the answer on a piece of paper without letting anybody see it and seal it in an envelope. Have somebody hold the envelope and at the end ask him to open it and reveal the number you wrote at the beginning. Wow, Magic!
2. Magic Maths Trick
Guess how much money people have in their pockets!
Without giving you any information, ask a friend to count the value of some coins and write the amount on a piece of paper. Then ask your friend to:
Double the amount.
Add the first odd prime number to the new total.
Multiply the result by 1/4 of 20.
Subtract the lowest common multiple of 2 and 3.
For the grand finale, you ask for the final answer. Take off the last digit and you will be able to work out how much the coins are worth!
3. Magic Mathematical Trick
Amaze your audience by working out not only their ages but also what size shoes each wears! Wow them even more by telling them how the maths works.
Give them the following directions but tell them not to show you any calculations:
Write down your age.
Multiply it by 1/5 of 100.
Add on today’s date (e.g. 2 if it’s the 2nd of the month).
Multiply by 20% of 25.
Now add on your shoe size (if it’s a half size round to a whole number).
Finally, subtract 5 times today’s date.
Show me your final answer!
Look at the answer; the hundreds are the age and the remaining digits are the shoe size. If for instance somebody shows you 1105, there are 11 hundreds—the age, and the remaining digits 05 (or 5) show the shoe size.
4. Magic Mathematical Trick
Mind Reader
A little bit of algebra explains this ‘magic’. Ask a friend to pick 3 consecutive numbers with none greater than 60 (say for example, she picks 42, 43, 44). Ask her to tell you a multiple of 3 that is less than 100 (for example, 39). Then ask her to add the four numbers and multiply by 67, not letting you see the numbers of course, and to tell you the last two digits of her answer. Now you can really amaze her by giving the whole answer and the three consecutive numbers used at the start.
This is what you do. Your friend gives you a 2-digit number and you double it to get the remaining digits. In this case the calculation is
42+ 43 + 44 + 39 = 168, 168 x 67 = 11256
You are told the last two digits, namely 56, and you can immediately give the whole answer 11256.
To get the three consecutive numbers, you divide her multiple of 3 by 3 and add 1 (e.g. 13+1=14). Subtract this from the two-digit number she has given you and you get the first of the three consecutive numbers in question (e.g. 56 -14 = 42).
