Arun & Bijay can make paintings in 3 days, Bijay & Chandan can make those paintings in 5 days. If Arun, Bijay & Chandan together can finish the work in 2 days, then Arun & Chandan together will do it in ________ days.

Correct option is C

Given:
Time to complete the whole work by Arun and Bijay together = 3 days
Time to complete the whole work by Bijay and Chandan together = 5 days
Time to complete the whole work by Arun, Bijay and Chandan together = 2 days
Formula Used:
$$\text{Efficiency} = \frac{\text{Work Done}}{\text{Time Taken}}$$​​
Solution:
Let the total work be LCM of 3, 5, 2 i.e. 30 units.
Let efficiency of Arun, Bijay and Chandan be A, B and C respectively.
=> Efficiency of A + B = $$\frac{30}{3}$$​ = 10 units/day ----(i)

=>Efficiency of  B + C = $$\frac{30}{5}$$​ = 6 units/day ----(ii)
=>Efficiency of  A + B + C = $$\frac{30}{2}$$​ = 15 units/day ----(iii)
=> 10 + C = 15
=> C = 5 units/day
B + C = $$\frac{30}{5}$$​ = 6 units/day
=> B = 6 - 5 = 1 unit/day
A + B = $$\frac{30}{3}$$​ = 10 units/day
=> A = 10 - 1 = 9 units/day
Efficiency of Arun and Chandan together =  A + C = 9 + 5 = 14 units/day
Time taken by Arun and Chandan = $$\frac{30}{14} = \frac{15}{7}$$​ days