A, B and C can do a work on their own in 5, 10 and 15 days respectively. Calculate the time required by B and C to do it together.

Correct option is D

Given:
A, B, and C can do the work on their own in 5, 10, and 15 days respectively.
Solution:
Total work = LCM of 5, 10, and 15= 30 units
Efficiency of B =  $$\frac {30}{10}$$​ = 3 unit work in 1 day

Efficiency of C =  $$\frac {30}{15}$$​ = 2 unit work in 1 day
Efficiency of B and C together = (3 + 2) = 5 unit work in 1 day
 Time taken to complete the work by B and C = $$\frac {30}{5}$$​ = 6 days.