Ketan and Kunal can complete a job together in 7 days. Kunal is $\frac{7}{4}$ times as efficient as Ketan. In how many days can Kunal alone complete the job?

11 days

Ketan + Kunal = 7 days,

Ketan : Kunal = 7 : 4  (Efficiency)

⇒ They both working together can complete a work in 7 days = (7+4) x 11 = 77 units,  ..(Efficiency × Days = Total work)

⇒ Time required by Kunal to complete the work alone = \(\frac{77}{7}\) = 11 days,    ..(\(\frac{Work}{Efficiency}\) = Time)