Correct Answer - Option 2 : 52.5
A is 50 times more efficient than B and C is 100 times more efficient than B. A and C can finish a work in 15 days.
If A and B can together finish it in t days with A and B finishing the work in a and b days respectively,
1/a + 1/b = 1/t
Let efficiency of B be 100.
Then A = 150
Work efficiency of A = 3
Work efficiency of B = 2
Work efficiency of C = 4
So, ratio of efficiency of A: B: C = 3 : 2 : 4
A and C can finish a work in 15 days
Total work = efficiency × time
= 7 × 15 = 105
Time = 105/2 = 52.5 days