Consecutive number trick–
Ask a person to think of a number from 1 to 10, add on the number directly after it and add on the number directly after that then ask them to tell you the result of their addition and you can easily tell what the three numbers were because, as you can see, all the results of adding three consecutive numbers are different.
Why only consecutive numbers? Because you cannot do this trick with just any three numbers. Say for example the participant tells you the number 12, then their three numbers could be 6, 4 and 2 or 7, 3 and 2 or some other combination of numbers that add up to 12.