Civil Service Exam Reviewer · Ratio and Proportion · hard
A box has red and blue balls in the ratio 7 : 4. After 5 red balls are removed, the ratio becomes 37 : 24. How many blue balls are in the box?
- 42
- 66
- 29
- 24
Answer
D. 24
Solution
Red = 7k, blue = 4k. (7k − 5)/4k = 37/24 → k = 6. Blue = 4 × 6 = 24.
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