Q) 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: 

a) 9 1/5 days            b) 9 2/5 days             c) 9 3/5 days             d) 10 days
Ans:

A’s 1 day’s work = 1/16

B’s 1 day’s work = 1/12

∴ (A + B)’s 1 day’s work = 1/16 + 1/12 = 7/48

∴ (A + B + C)’s 1 days work = 1/4

∴ C’s 1 day’s work = 1/4-7/48 = 5/48

∴ Time taken by C alone to finish whole work = 48/5 = 9 3/5 days

Hence, Answer is [C].

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