Time and work Quantitative aptitude question

[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 how much days?
(a) 9 (1/5) days
(b) 9 (3/5) days
(c) 9 (2/5) days
(d) 9 (4/5) days

Solution

Answer   (b)
Explanation
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Amount of work A can do in 1 day = 1/16

Amount of work B can do in 1 day = 1/12

Amount of work A, B and C can together do in 1 day = 1/4

Amount of work C can do in 1 day = 1/4 - (1/16 + 1/12) = 3/16 – 1/12 = 5/48

=> Hence C can do the job on 48/5 days = 9 (3/5) days