How do they do online card tricks?

Question

like when you think of a number and then you click next or w.e and the number comes up. like HOW THE HECK do they do that??? if you need an example go to http://www.ecardtricks.com/ and click on mind reader 3.

Answer 1

well, they involve things such as color and shapes to deduce the number you chosen

By telling them those attribute, the question are deducing towards the number you choose

For example, they ask you what color was your number, in which of this shape has your number.

It looks as if you are picking a group of numbers, but actually in each group, there's only one unique number. The other numbers are "misdirection"

you are basically telling them what number you choose by picking those answers