Raju, Shobh and Mohan can do a work in 15 days, 20 days and 25 days respectively. In how many days, will the work be finished, if they do it on alternate days?

$18 \frac{9}{10}$ days

If A, B, C start working on alternate days

by considering them as a single block of eff = 47 

in 6 x 3 days, work done = efficiency x no. of days 

                                    = 47 x 6  

                                    = 282

Remaining work = 300 - 282 = 18

This will take A = \(\frac{18}{20}\) =  \(\frac{9}{10}\) days

Total time taken to finish the complete work = 18\(\frac{9}{10}\) days