Missing Number

Without looking at your friend, ask him/her to write down any number that is at least four digits long. Example :  13579 Then ask your friend to add up the digits. 1+3+5+7+9 = 25 Now subtract this answer (25) from the first number. 13579 - 25 = 13554 Ask your friend to cross out one digit from the answer. (You can not cross out a zero) 1X554 Now ask our friend to slowly read out the digits that are left. 1554 You now magically say : "The missing number is three." How to do the missing number math trick This is a power of 9 trick. Once your friend crosses out a digit and reads out the digits that are left,  you simply add them up. Example : 1+5+5+4 = 15 You now add on to your answer to get the next number that divides by nine! The next number to divide by 9 after 15 is 18. Therefore you need to add on three. This is the number that was crossed out!