Ashutosh can complete an assignment in 14 hrs and Siya can do it in 10 hrs. Together with Rahul , they completed the work in 5 hrs. Then, how long does Rahul alone take to do the assignment?

35 hrs   

Let total work = 70,

Efficiency of Ashutosh + Siya + Rahul = \(\frac{Total\; work}{No.\; of \;hrs}\)

                                  = \(\frac{70}{5}\) = 14

Efficiency of Rahul = eff(Ashutosh + Siya + Rahul) - eff(Ashutosh) - eff(Siya) = 14 - 5 - 7 = 2

Time taken by C alone = \(\frac{Total\; work}{Efficiency}\)

                               = \(\frac{70}{2}\) = 35 hrs