The ratio of red to blue marbles in a bag is 5:3. If there are 24 blue marbles in the bag, what is the total number of marbles in the bag?

✓ Correct Answer: Option B

If 3 parts (blue marbles) correspond to 24 marbles, then 1 part = 24/3 = 8 marbles. The total ratio is 5+3 = 8 parts. So, total marbles = 8 parts * 8 marbles/part = 64.