A can complete a task in 10 hrs whereas B is 5/4 efficient as that of A & C is twice efficient as that of B. In hw many days they could cmplt the task by working together.
B is 5/4 times efficient as A means B can complete the task in 10(4/5)= 8 hours
C twice as efficient as B means C can complete the task in 4 hours
So efficiency of A, B and C= 1/10+1/8+1/4= 4+5+10/40=19/40
They can compete the task in 40/19 hours, ie 40/(24x19)=5/57 days.