Allyndreth showed Branwyn a number trick. She said, Think of the number of times you bathed last week. Multiply by 2. Add 5. Multiply by 50. If youve already had your birthday this year, add 1,750. If you havent already had your birthday this year, add 1,749. Add the last two digits of the current yearso if this year is 2012, you should add 12. Then subtract the four-digit year in which you were born. Branwyn did each step correctly and then told Allyndreth the answer: 722. Allyndreth said, You bathed seven times last week and you are 22 years old. Branwyn was amazed, but Allyndreth told her it was just a stupid number trick. Try it for yourself. Then use algebra to figure out why it works.