I can read your mind

Logic Level 1

Think of any finite number. \large{\text{Think of any finite number.}}

Add 21.
Double it.

Remember it. \large{\text{Remember it.}}

Now take your original number again.
Half it.
Subtract 42.

Remember it. \large{\text{Remember it.}}

Now take your second result and subtract it from your first result four times.

Enter your answer \large{\text{Enter your answer}}


The answer is 210.

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John M. by John M. , 24, USA

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3 solutions

Discussions for this problem are now closed

Bilel Mabrouk
Jan 12, 2015

In such "mind-reading" tricks , the result does not depend on your chosen number

let x be that number , the final result equals 210 no matter what x is : 2 ( x + 21 ) − 4 ( x 2 − 42 ) = 2 x + 42 − 2 x + 168 = 210 2(x+21)-4(\frac { x }{ 2 } -42)\\ =\\ 2x+42-2x+168\\ =\\ 210

54 Helpful 1 Interesting 2 Brilliant 1 Confused

Mind=Read! :v

Prasun Biswas - 6 years, 5 months ago

You can read everyone's mind!!!

Samuraiwarm Tsunayoshi - 6 years, 5 months ago
Roy Tu
Jan 13, 2015

Take your number to be 84 and save yourself some trouble. Second answer becomes 0, first answer becomes ( 84 + 21 ) ∗ 2 = 210 (84+21)*2=\boxed{210}

7 Helpful 0 Interesting 0 Brilliant 0 Confused

2(x+21)-4(1/2 x-42) = 2x+42-2x+168 = 210

2 Helpful 0 Interesting 0 Brilliant 0 Confused

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