I've got a bit of a problem, and I thought this forum might be a cool place to post it, saying as y'all seem to like math and (I'm guessing) probably have some experience with roleplaying systems in general.

I'm trying to break down the system in order to get an understanding of what odds my players have in any given situation, I'm trying to find an equation which represents WoD dice rolls. It seems like it should be trivial, but I'm clearly missing a step somewhere.

WoD dice work in this way:

You roll a number of dice (X), and you are attempting to get at least a specific number of "successful rolls" (Y).

A successful roll is anything >7. So 8, 9 and 10 are considered successes.

I.e. Bob needs to get 1 success in order to accomplish his task, he has 3 dice to roll which represents his skill. If any of them succeed, he succeeds. If he needed 2 successes, then 2 of the dice would need to roll successes in order for him to succeed.

Easy, 30% chance of success, X attempts, Y successes.

Here is where I'm getting thrown however. "10 again".

In the WoD system there is another factor called "10 again". Where if the player rolls a 10 on any previous dice, he gets to roll another dice for each 10, technically meaning you can get 10 successes from a single dice (it's just extremely unlikely), and I simply cannot factor that into the solution.

For example. Bob has 3 dice to roll. He needs 5 successes. A seemingly hopeless task that should be beyond his skill to accomplish under normal circumstances. Luck is on his side however, and he rolls 10, 10, 8.

3 successes, and 2 more rolls!

He rolls his 2 dice, one falls short at 3, but the other is another 10, giving him another success and another roll.

His final roll comes up 9 and he succeeds in his hopeless task, the bullet he was firing ricocheting off the floor and catching the thug in the scrotum in an amazing stroke of luck.

Shouldn't be the hardest question in the world, but I've spotted some easier, so enjoy.

(Mods: Feel free to move this into Games or Mathematics, I wasn't sure exactly where in the 3 forums it should go. I felt this was most fitting but if you feel otherwise, I apologize.)