Let your friend think of the number of the month he was born in. Ask him to multiply this by 2,and add 5, multiply this by 50 and add his present age. Ask him to tell you the sum. Then you tell him his age! Not only that, you tell him the month he was born in and add to his suprise!
As your friend tells you the sum, silently subtract 250 from it. The last two numbers of the figure are his age and the first number indicates the month of his birth.For example let the age be 40 and the month, October.
The last two digits indicate his age, the preceding digits show the number of the month he was born in.