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I am just 18, completely naive and new to the world of maths. I have made a few math tricks based on this trick (or tricks of this format - with the exact calculations and steps involved):

 TRICK:                                 SOLUTION: STEP 1: Take a secret number.          Let it be denoted by ‘x’. STEP 2: Multiply by 5.                 => 5x STEP 3: Add 25.                        => 5x +25 STEP 4: Divide by 5.                   => (5x+25)/5 = x+5 STEP 5: Subtract your secret number.   => x+5-x= 5 Your answer is always 5.               = 5 

I am thinking of writing a paper on what I have made, but even after extensive searching on net, Google, Google Scholar and also websites like jstor.org, I am not able to find any material related to this exact math trick.

Can someone help me out here? Is it just that this trick is age old, and may be comes under "Creative Commons" (if that makes sense)?

I was in 8th when I figured it out, I know that it can be done by 6th grader, but it's not about this trick, it's about the 20 odd tricks made by me (based on this trick), some of which involving trigonometry and log too. I am writing a paper and I think it would be great if I find a reference to quote for this trick.

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    I meant the number of thousands - I can have 153 thousands if I like.2012-06-22

1 Answers 1

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The "trick" is just linearity: $\rm\ f^{-1}(f(x)\!+\!f(n))\, =\, x\!+\!n.\:$ Above $\rm\ n=5,\ f(x) = 5x,\ f^{-1}(x) = x/5.$

Such simple consequences of linearity of multiplication are very well-known to mathematics students, but they may not be so obvious to a layperson - especially if disguised more effectively.

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    I know it already, I know how the trick works and I know that it is never supposed to amaze mathematicians. I have made tricks based on this trick as a school student, and I know that it will amaze school/undergraduate students and their teachers $f$or ever.2012-06-22