A jar contains only red and blue marbles in a ratio of 3:7. If there are 21 blue marbles, how many red marbles are there?
- A. 9 ✓
- B. 6
- C. 14
- D. 12
Correct answer
A. 9
Explanation
The ratio 3:7 means for every 7 blue marbles, there are 3 red. 21 blue ÷ 7 = 3 groups, so red marbles = 3 × 3 = 9.
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