Given: Efficiency ratio of A and B is = 3 : 4 A alone can compete a work in = 20 days Formula: Total work = Efficiency × Time Calculation: Let A does 3 units of work and B does 4 units of work. Total work = 3 × 20 = 60 unit ∴ Time taken by B to finish the whole work = 60/4 = 15 days