DRDO Multi tasking staff Model paper 6

Let the time taken by Ram, Aman, and Chandan alone to finish the work be ‘x’, ‘y’ and ‘z’ days respectively.
According to the question ∶
(1/x) + (1/y) = (1/7.2) ----(1)
(1/x) + (1/y) + (1/z) = (1/4) ----(2)
From (1) and (2) ∶
(1/z) = (1/4) – (1/7.2)
(1/z) = (1.8 – 1)/7.2
z = 9 days
Hence, time taken by Chandan alone to finish the work = 9 days
Thus, the correct answer is option 3.