Correct Answer - Option 1 : 3

**Given:**

A is twice as efficient as B

B is thrice as efficient as C

C alone can do work in 30 days

**Concept Used:**

Total work = Time taken × Efficiency

**Calculation:**

A = 2B

B = 3C

A ∶ B = 2 ∶ 1

B ∶ C = 3 ∶ 1

A ∶ B ∶ C = 6 ∶ 3 ∶ 1

C alone can do work in 30 days

So, total work = 1 × 30 = 30 units

Efficiency of (A + B + C) = 6 + 3 + 1 ⇒ 10 units

**∴ Work completed by A, B and C = 30/10 = 3 days**