115. A can lay railway track between two given stations in 16 days and B can do the same job in 12 days. With help of C, they did the job in 4 days only. Then, C alone can do the job in:

✅ The correct answer is option C.
(A + B + C)’s 1 day’s work =
1
,

4

A’s 1 day’s work =
1
,

16

B’s 1 day’s work =
1
.

12

C’s 1 day’s work =
1
–

1
+
1

=

1
–
7

=
5
.

4
16
12
4
48
48

So, C alone can do the work in
48
= 9
3
days.

5
5