2018 · Q42
An alloy A contains two elements, copper and tin in the ratio of 2:3, whereas an alloy B contains the same elements in the ratio of 3:4. If 20 kg of alloy A, 28 kg of alloy B and some more pure copper are mixed to form a third alloy C which now contains copper and tin in the ratio of 6:7, then what is the quantity of pure copper mixed in the alloy C?
Elementary MathematicsRatio and Proportion
- A3 kg
- B4 kg
- C5 kg
- D7 kg
Explanation
Alloy A contributes 8 kg Cu + 12 kg Sn (from 20 kg at 2:3); alloy B contributes 12 kg Cu + 16 kg Sn (from 28 kg at 3:4). With x kg of pure copper added: (20 + x)/28 = 6/7 gives 140 + 7x = 168, so x = 4 kg, option (B).