Civil Service Exam Reviewer · Ratio and Proportion · hard
A box has red and blue balls in the ratio 3 : 7. After 10 red balls are removed, the ratio becomes 1 : 4. How many blue balls are in the box?
- 24
- 80
- 66
- 56
Answer
D. 56
Solution
Red = 3k, blue = 7k. (3k − 10)/7k = 1/4 → k = 8. Blue = 7 × 8 = 56.
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