Ashish can do a piece of work in 30 days. He starts the work and continues for 5 days, then Bilal joins and together they work for 5 more days to complete the work. Find the time taken by Bilal to complete the work alone.

7.5 days

Ashish's work of 1 day = \(\frac{1}{30}\)

Work done in 5 days = \(\frac{5}{30}\) = \(\frac{1}{6}\)

Therefore, one - sixth of the work is done 

Remaining work is done by Ashish and Bilal together in 5 days 

Ashish and Bilal will complete the total work in 6 days

Efficiency of Bilal = 5 - 1 = 4

Time taken by Bilal alone to complete the work = \(\frac{Total\; work}{Efficiency}\)

                                                                = \(\frac{30}{4}\) = 7.5 days