Painter A can paint a house in 40 days and Painter B can do it in 60 days. With help of C, they did the job in 20 days only. Then, C alone can do the job in

Let the total work to be done = 120 units

A's efficiency = $$\frac{120}{40} = 3$$ units/day

B's efficiency = $$\frac{120}{60} = 2$$ units/day

Let C's efficiency = $$x$$ units/day

A, B and C complete the work together in 20 days

=> $$(3 + 2 + x) \times 20 = 120$$

=> $$5 + x = \frac{120}{20} = 6$$

=> $$x = 6 - 5 = 1$$

$$\therefore$$ Time taken by C alone to complete the work = $$\frac{120}{1} = 120$$ days

=> Ans - (A)