Math: Probability, please help. (Chance of something happening if you do it twice.)?

If you, for example, take two dice and roll them both at the same time, what is the chance that at least one will be a six? I'm wondering, because if you just add 1/6th+1/6th, you get 1/3rd. Which is fine and dandy, but what if you roll those two dice 6 times? You get 1. Yet you could at the same time not... show more If you, for example, take two dice and roll them both at the same time, what is the chance that at least one will be a six?

I'm wondering, because if you just add 1/6th+1/6th, you get 1/3rd. Which is fine and dandy, but what if you roll those two dice 6 times? You get 1. Yet you could at the same time not once roll a six even if you rolled 50 times. I understand the probability would go up, but never be 1. I'm looking more for the formula, rather than just someone telling me what I'm doing wrong.
Update: Thank you; :D.

I knew 1/6th * 1/6th, but I did not know about the complements, thank you; that helped a lot.

So..

49/50 * 49/50 = 2401/2500ths. .. or 99/2500ths? Roughly 1/25th?
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