[TwinnSplitter]

Basically, you want to use the way that will allow you to use the least number of probability calculations. So, for example, if it asks "what is the probability that you get at least one blue", then the options are that you get 1 blue or you get 2 blues. However, instead of calculating each of these individual probabilities, it is easier to calculate
1 minus the probability of getting 0 blues.

But in the case where it says what is the probability of getting 0 blues, then it's easiest to just use the probability of getting two "not blues".

And if it asked you what is the probability of 2 blues, then it would be easiest to just find it as (2/8) x (1/7) = 1/28.

In other words, just think which way will take you the smallest number of probability caclulations.

Hope that helps.