A bag contains 5 red marbles, 3 blue marbles, and 2 green marbles. If one marble is selected at random, what is the probability that it is blue?

Step 1: Find the total number of marbles.

There are:
5 red marbles
3 blue marbles
2 green marbles

Total = 5 + 3 + 2 = 10

Step 2: Identify the favorable outcomes.

We want to select a blue marble.

There are 3 blue marbles, so there are 3 favorable outcomes.

Step 3: Use the probability formula.

Probability = favorable outcomes / total outcomes

P(blue) = 3 / 10

Step 4: Express the result if desired as a decimal.

3 / 10 = 0.30

Therefore, the probability of selecting a blue marble is 3/10, or 0.30.