A can lay a railway track between two stations in 20 days, B can complete the same task in 15 days, and C assists them to finish the job in 5 days. How long would it take for C to complete the job on their own?
Show answer & explanation
Correct answer: C
Explanation
The correct answer is option 3 i.e. 12 days.
A's work rate = 1/20
B's work rate = 1/15
(A + B + C)'s combined rate = 1/5
C's work rate = 1/5 - (1/20 + 1/15) = 1/5 - 7/60 = 1/12
Time for C alone = 1/(1/12) = 12 days