Meredith starts a saving fund for her son. She deposits $10 on his first birthday, $20 on his second, $30 on his third and so on....for 40 years (wow, is he still going to be living with her, too? Lol *ahem*....).

Use to determine how much she will have deposited in total (ignore interest at this point).

I don't understand how to plug this into the formula, example:

, which equals $320, but logic tells me that $10 + $20 +30, only equals $60.

What am I missing?