P, Q and R can complete a task together in 15 days. P and R can complete the task together in 40 days. In how many days can Q complete the task alone?

24 days

P + Q + R = 15 days,

P + R = 40 days,

⇒ P + Q + R = 8

⇒ 3 + Q = 8 

⇒ Q = 5,

Therefore, time required for Q to complete work alone = \(\frac{120}{5}\) = 24 days,      ..(\(\frac{Work}{Efficiency}\) = Time)