Correct Answer - Option 1 : 3 : 11

**Given:**

The ratio of copper to tin of 1^{st} alloy = 3 : 4

The ratio of copper to tin of 2^{nd} alloy = 1 : 6

Weight of 1st alloy = 7 kg

Weight of 2nd alloy = 21 kg

**Calculation:**

The quantity of copper in 7 kg alloy = (3/7) × 7 = 3 kg

The quantity of tin in 7 kg alloy = (4/7) × 7 = 4 kg

The quantity of copper in 21 kg alloy = (1/7) × 21 = 3 kg

The quantity of tin in 21 kg alloy = (6/7) × 21 = 18 kg

New alloy = 1^{st} alloy + 2^{nd} alloy

Total quantity of copper in new alloy = 3 + 3 = 6 kg

Total quantity of tin in new alloy = 4 + 18 = 22 kg

The ratio of copper to tin in new alloy = 6 : 22 = 3 : 11

** ∴ The ratio of copper to tin in the new alloy is 3 : 11.**