Today in econmomic class we were talking about bonds where you give your money to the government and over a certian(sp) period that money doubles, well the teacher didn't say how long that time is, so my question is

How long will I have to wait if I don't happen to buy a bond?

I'm 17, so I'm assuming I won't be able to buy one so I would give the money to my grandmother and have her buy it for me

There are many forms of bonds but I will refer to two general bonds. The first one is regular bond issued by companies, not the government. They have higher interest rates because there is more risk involved. Then there are treasury bonds which are what you referenced. These bonds carry a lower interest rate because there is essentially no default risk. In other words, the US won't go bankrupt (not to get into a debate on the national deficit) and these bonds will always be redeemable. Not every bond is going to double your money, in fact, there are many better ways of doubling your money. To figure out the present value of the bond on a financial calculator (I don't remember the exact equation because I use calculators) you use the number of periods, the interest rate, the future value of the bond, and the pmt amount, to get the present value. Realize though that bonds aren't like stocks in the sense that the selling value increases over time. What happens is that they make payments to you every month and than at the end of the bonds term you get your money back. Where as in the stock market the value of your purchase can actually increase in value so when you sell them you get the current value.