Example: Mentalist Trick (2)
(related to Part: Tricks for Mental Maths)
You can use your mentalist power to impress people by guessing the number they have thought:
 Ask somebody to think a number between \(1\) and \(100\).
(e.g. \(41\))
 Ask your partner to double the number.
(e.g. \(41\cdot 2=82\))
 Next, she/he should add \(5\) to the result.
(e.g. \(82 + 5=87\))
 Next, she/he should multiply the result by \(10\) and tell you the result.
(e.g. \(87\cdot 10=870\))
Finding out the number thought by your partner
Now, pretend to use your "mentalist powers" and without explaining, what you are doing, perform the following calculations:
 Calculate the half the result mentally.
(e.g. \(870 / 2=435\))
 Cancel the last digit
(e.g. \(43\not 5=43\))
 Subtract \(2\) and tell the result
(e.g. \(43  2=41\))
Think about, why this trick always works. If you have a solution, edit this article correspondingly, or provide a comment.
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