Answer
3/10
Work Step by Step
P(event)=$\frac{numberoffavorableoutcomes}{numberofpossibleoutcomes}$
The number of favorable outcomes is 3 of blue, so it will be the number of outcomes for finding the probability.
P(event)=$\frac{numberoffavorableoutcomes}{numberofpossibleoutcomes}$
P(blue)=$\frac{3}{3+7}$ -simplify-
P(blue)=$\frac{3}{10}$