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**Ploppies** I have not learned this in school yet, so have no idea how to do this, nor does my maths teacher. For an assignment i am talking about a mental disorder and thought it would be cool to show how many years it would take before you have a 25% and 50% chance of experiencing it.

This particular disorder effects a random 1/200 people each year. I need to know how to calculate this :S is there some particular formula someone would be able to show me?

Thanks very much for any help