math people: can you tell me how this website reads your mind?

[Maximus96]

mystic ball this site reads your mind supposedly. i understand that the secret number you come up with will always be multiples of 3, but how does it know which number you're thinking of?

 

[notfred]

Because every possible answer has the same symbol next to it. Try it with any number - they all have the same symbol.

 

[chuckywang]

oh, this thing again. it's pretty simple...the possible values you end up with are all multiples of 9. Alas, they are all the same symbol in the chart.

 

[blackdogdeek]

any 2 digit number can be written as 10t + u. eg - 23 = 10(2) + 3.

so the instructions say to add the digits and then subtract the sum from the original number:

10t+u - (t+u)

this simplifies to:

10t - t +u - u

which simplifies to:

9t

so the answer will always be a multiple of 9. if you look at all the multiples of 9 in the chart, they are the same symbol.

 

[Maximus96]

oh i see. the symbols also change everytime it reloads. thanks

 

[chuckywang]

Originally posted by: blackdogdeek
if you look at all the multiples of 9 in the chart, they are the same symbol.

well, except for 90 and 99. but those numbers can never be the number you end up with.