How do u work out this maths equation?

My boyfriend does a little trick, he asks me and friends to think of a number, double it, half it, times it by 2 etc etc (not sure on the order) and we always come out with the same number?? how is this possible? can someone please tell me how this is done??? he claims it is ''magic''How do u work out this maths equation?
when you double something and divide it by 2, you will get the same number. 15*2=30


30/2=15


or he tells you to multiply by nine and add the two digits.


this way, both of you get nine let's say you pick 4


4*2=8


8*9=72


7+2=9


this works with every numberHow do u work out this maths equation?
Obviously if you double and half you get back to the number you started with. He's doing a more complicated version of that where it's not so obvious.


For example, 2(x+3)=2x+6.


If you add 3 to a number then double it's obvious that if you then halve it and take 3 you get back to the number you started with. But you could take 6 and halve it and that would also get you back to what you started with but it's not so obvious so it can seem like magic.





So if I say, think of a number, add 3, times 2, take 6, divide by 2, you'd get back to the same number you started with. All because of the identity above.





If you use a more complicated identity it can seem even more amazing.
Think of a number.Add two.Triple the result.Double the result.Divide by six.Subtract the original number? Yes. Say that my number was 12. 12 plus 2 is 14. Right? 14 times 3 is 42 (triple number) and 42 doubled would be 84. 84 divided by 6 is 14, my original number.





No matter what number that you choose you keep doing opposite operations so that the number comes out the same : )
It's not magic, just a list of operations that ends up leading to the same number.





I could tell you:


think of a number


now add 2


now subtract 2


And you get the same number! It's magic!





What your boyfriend does is kind of the same thing, only more complicated.
its a trick...





like not magic...





but what happens is there is a sum and whatever number you start with it always ends up with the same number at the end.





sorry but i dont know the sum! search the internet...





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well doubling it then halving it makes the same number... like if u picked 16... then doubled would be 32... then divide 32 by 2 and u get 16... etc...





lol math is never magic; thats why its math.

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