TrulyDevious
Expanding on from what sin(pi) said, all of which is correct, a more general and less formulaic approach is to multiply the chances of each event happening together to get the probability of all events happening. For example, Focus Blast has a functional 7% chance to get a special defense drop. Let's see why:

Focus Blast has 70% accuracy, so the chance of it hitting is 7/10. It has a 10%, or 1/10, chance of dropping special defense. Multiplying the two gives 7/100, or 7%.

Now let's try a complicated example: What is the chance that Jirachi will paralyze Latios with Body Slam and Latios will be unable to move in the next two turns due to either Iron Head's flinch or paralysis?

Body Slam has a 3/5 chance to paralyze with Serene Grace. In the following turns, Latios has a 1/4 chance of full paralysis and a 3/5 chance of a flinch. However, we add the chance of flinch and chance of paralysis together before multiplying, since both result in the desired outcome of Latios not moving. This gives 17/20. We then square this number, since we're dealing with the next two turns, to get 289/400. However, we also want Body Slam to paralyze on the first hit, which is a 3/5 chance. Another multiplication gives 867/2000, which is 43.35 %.

A final and generalized example: What is the chance that a burn will not happen after n Scalds?

Although seemingly complicated, this is quite simple. The chance of a Scald burn not happening is 7/10, and we are dealing with this same probability n times So the result is 7/10 x 7/10 x 7/10 ..., or (7/10)^n.

Kinda long and wordy but I hope we both helped!