How can you tell the age of your friend

1.Ask his or her to right his age :- say 16
2.then double it making 32
3. add 1 to it , making  33
4.Multiply it by 5 making 165
5.now at 5 to eat making 170
6.Now multiply it by 10 making 1700
7.then subtract 100 making it 1600
8.now ask him to tell the number.
9. you delete the last two digits the remaining number will be his or her age that is 16.