Simple Interest function?

I wondered if iWork 09 has a function that calculates simple interest? i.e.:

I put £100 in a bank account that pays 5% interest each year. How much money will I have at the end of 5 years.

The answer of course is: (((((100 1.05)*1.05)*1.05)*1.05)1.05)

I have looked through the function help but I can't find anything that would help me although there is a load of rubbish in there to do with bonds and securities that I'm sure the average person uses everyday. My neighbour, an 83 year old woman, spends her time dealing in bonds when she's not round her friends house drinking tea. And when she is round her friends house drinking tea all they talk about is bond trading. Obviously.

I'm actually trying to work out how much things will cost in the future due to inflation. Some items I need to replace in 3 years, others 5. I then need to divide the answer by the number of years things have to be replaced so I know how much money to put aside each year for wear and tear.

I'm seriously thinking of jumping ship to either Excel, OpenOffice or Google Docs. I need some sort of Goal Seek and I need simple equations.

Numbers needs some serious work, as it is, it is a pig pile of steaming pooh. I'm downloading OpenOffice as I type this ....