Civil Service Exam Reviewer · Ratio and Proportion · hard
A box has red and blue balls in the ratio 3 : 7. After 11 red balls are removed, the ratio becomes 1 : 28. How many blue balls are in the box?
- 28
- 12
- 40
- 39
Answer
A. 28
Solution
Red = 3k, blue = 7k. (3k − 11)/7k = 1/28 → k = 4. Blue = 7 × 4 = 28.
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