X and Y are two alloys of copper (Cu) and zinc (Zn). Alloy X is prepared by mixing Cu and Zn in the ratio 5:4, and alloy Y is prepared by mixing Cu and Zn in the ratio 5:13 respectively. If equal quantities of alloys X and Y are melted to form a third alloy Z, then what is the ratio of Cu to Zn in Z?
- A. 5:8
- B. 5:7 ✓
- C. 6:7
- D. 7:8
Correct Answer: B. 5:7
Explanation
Assume equal quantities of 18 units each (LCM of 9 and 18). In X, Cu = \frac{5}{9} \times 18 = 10, Zn = 8. In Y, Cu = \frac{5}{18} \times 18 = 5, Zn = 13. Total Cu = 10 + 5 = 15. Total Zn = 8 + 13 = 21. Ratio = 15:21 = 5:7.
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