The Chosen Number (Math Brainteaser Puzzle)

Ask a friend to think of a number and ask then ask him to :

multiply it by 5

add 6

multiply the result by 4

add 9
multiply the result by 5

Ask him what the result is and you will immediately be able to tell him what the number he had chosen was.

How to do it: subtract 165 from the result and take off the two zeroes at the end of the number you get. This will leave you with the original number.