I know somebody who can do this trick where he asks you to think of a number, add some stuff, subtract some stuff and then he guesses the final number. Now at first, this was not an exciting trick as anyone can always make the number come out to be say, 25. But he changes the number every time! Wondering if anybody knows and is willing to share the secret...
In the version of the original trick, the teller may follow a long sequence of instructions, but somewhere in the sequence the teller will ask you to remove the number you first thought of - thus deleting the only variable the teller did not know. The residual answer is the combination of 'add X / multiple by Y / take away Z' etc that the teller can remember in his head. The teller thus knows the answer.
The simple version of the trick follows the same combination of 'add X / multiple by Y take away z' etc so the end answer is consistent.
But for a teller that can juggle numbers in his head, the teller can vary the instructions and just keep track of the residual number at all times.
You can do it this way.Get the person to do some +ing and -ing to his number X (eg X+8..-2...-.5...+1).He will have now X+2.This +2 is now known to you! Now get him to multiply his result by 10 (say, in 2 stages-by 5 then by 2).Note well that that +2 onto his X,when multiplied by 10,will account for 20 in his result.Ask to minus 20.The result is now X multiplied by 10.As soon as he gives the result,drop the end zero and say what is left-very quickly.
... think of a number...... double it....... add 50....... half it...... take ur original number and subtract it from the number you have now..... you should be left with 25.
this way is, i think, the best as the trick is that end result is half of the number that u ask them to add ( i ask them to add 50, the result is 25.) and you can ask them to add any number and they will get confused every time... ive messed with so many minds with this..
its very obvious this way i normally tell it with a story like.
think of an amount any amount... one day you feel really luck and you decide to test ur luck on the slots and you double ur winnings...... coz your on a roll u place a bet and win X amount....... hyped up u go back to the slots to win some more but you loose half of it, ur lucks running out! and for one last go u bet the amount you had originally and you loose that too........ oh well... at least you have 1/2X amount in ur pocket.