Correct Answer - Option 2 : 52.5

**Given:**

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.

**Formula:**

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

**Calculation:**

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