Civil Service Exam Reviewer · Ratio and Proportion · hard
A box has red and blue balls in the ratio 2 : 7. After 10 red balls are removed, the ratio becomes 3 : 28. How many blue balls are in the box?
- 16
- 72
- 56
- 66
Answer
C. 56
Solution
Red = 2k, blue = 7k. (2k − 10)/7k = 3/28 → k = 8. Blue = 7 × 8 = 56.
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