Rahul and Shyam, working together, can do a piece of work in 5 hours; Rahul alone can do the same work in 15 hours. How much time will Shyam alone take to do that work?

7.5 hours

Rahul + Shyam, = 5 hours,

Shyam = 15 hours,

⇒Rahul + Shyam = 3  (Efficiency)

⇒ 1 + Shyam = 3,

⇒ Shyam = 2,

⇒ Therefore, Time required by Shyam to complete the work alone = \(\frac{15}{2}\) = 7.5 hours.     ..(\(\frac{Work}{Efficiency}\) = Time)