Simple Math Trick

1 When Is Your Birthday?
 Ask someone to follow these steps:
   1. Multiply the number of the month by 5.
   2. Add 7.
   3. Multiply by 4.
   4. Add 13.
   5. Multiply by 5.
   6. Add the day of the month.
   7. Subtract 205.
 The last two digits are the day of the month, and the
 first digit(s) is the month number. (To make this seem
 more amazing, have them tell you the result before they
 subtract 205, and you do that part in your head.)






2 Find Your Age and Change
 Tell a friend that with this trick you can tell him his age,
 and how much change (less than $1.00) he is carrying.
 The friend starts with his age and follows these steps:
   1. Multiply his age by 4.
   2. Add 10.
   3. Multiply by 25.
   4. Subtract the number of days in a non-leap year.
   5. Add in the change.
   6. Add 115.
 The first two digits are the person's age, and the second
 two digits are the change in his pocket. (As with the
 Birthday trick, you can get the number before the last
 stem, and do that one in your head.)