Question

Two alloys are made by gold and copper in the ratio of 7 ∶ 2 and 7 ∶ 11 respectively. Same quantity of both alloys are mixed and third alloy is made. In this third alloy, the ratio between gold and copper is equal to 
1. 7 ∶ 5
2. 7 ∶ 12
3. 14 ∶ 13
4. 2 ∶ 11

Answer 1

Correct Answer - Option 1 : 7 ∶ 5

Ratio of gold and copper in first alloy = 7 ∶ 2

Total units in first alloy = 7 + 2 = 9 

Ratio of gold and copper in second alloy = 7 ∶ 11

Total units in second alloy = 7 + 11 = 18

Same quantity of both alloys are mixed to make the third alloy

∴ Both the units of first alloy and second alloy should be same

⇒ Units of first allow =  9_x2, Units of second alloy = 18

Ratio of gold and copper in first = (7 ∶ 2)_x2 = 14 ∶ 4

Ratio of gold and copper in second alloy = 7 ∶ 11

∴ Ratio of gold and copper in third alloy = (14 + 7) ∶ (4 + 11) = 21 ∶ 15 or 7 ∶ 5

∴ The ratio between gold and copper is equal to 7 ∶ 5