If it takes 10 days to die a trench of 100 m long, 50 m broad, 10 m deep, what length of trench, 25 m broad, 15 m deep can be dug in 30 days?

Ans:

       D          L            B            D

      10        100         50           10

      30         x            25           15

     x=100*30*50*10/10*25*15

       = 400m