Explanation

In the bag of marbles, there are 3 red marbles and 7 white marbles, for a total of 10 marbles that are not blue. There are a total of 3 + 7 + 2 = 12 marbles in the bag.

Since probability is defined as the number of desired items divided by the total number of choices, the probability that the marble chosen is not blue is \(\frac{10}{12}=\frac{5}{6}\).
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5/6

As C(n,r) = n!/(r!(n - r)!) ,
P(not blue)=1-P(blue) = 1- C(2,1)/C(12,1)=1- (2/12)=5/6