Answer: A - Red.
The marble is most likely to be red, since half of the marbles in the bag are red. This means that there is a 50% chance of selecting a red marble.
To calculate the probability of selecting each color, we can divide the number of marbles of each color by the total number of marbles in the bag:
- Probability of selecting a red marble: 1/2 (50%)
- Probability of selecting a blue marble: 1/4 (25%)
- Probability of selecting a green marble: 1/6 (16.67%)
- Probability of selecting a yellow marble: 1/12 (8.33%)
Therefore, the red marble has the highest probability of being selected, followed by blue, green, and yellow in decreasing order of probability. The key for this question is keeping calm and reading carefully.