medium · GMAT Quant
A jar contains only red and blue marbles. When 12 red marbles are removed, the ratio of red to blue becomes 1:3. When 12 blue marbles are then added to that new mixture, the ratio of red to blue becomes 1:5.
How many red marbles were in the jar originally?
- 15
- 18
- 21
- 24
- 30
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