I just attempted to solve a problem that involved the title.
So, it turns out I was getting an incorrect answer b/c I computed the probability of getting a 3 as 2/6 as opposed to 2/7. I don't fully understand why the probability of getting a 3 would be 2/7 though.
If I think about it like if you had the numbers 1-6 in a bag and you want a 3 to come up twice as often, the probability would be like adding another 3 to the bag. Giving it a probability of 2/7 where as if you said the probability was 2/6 it would be like pulling out one number and substituting a 3 for it. This makes sense too me but, in the case of a dye you can't really add another side even though it is biased. So why isn't it 2/6? What does it mean for a dice to have a 2/6 probability of landing on one side as opposed to 2/7?