In a bag there are 3 red marbles, 2 blue marbles, and 5 green marbles. What is the probability of drawing a red marble on one draw?

• A. 1/3
• B. 3/10
• C. 1/2
• D. 3/7

Answer: (B)

This question tests basic probability with equally likely outcomes. There are 3 red marbles among a total of 10 marbles (3 red + 2 blue + 5 green). When you draw one marble, each marble has the same chance of being selected, so the probability of a red marble is the number of red marbles divided by the total marbles: 3/10. That means a 30% chance. The other fractions would imply a different total or a different count of red marbles, so they don’t fit this situation.