A) 30 days
B) 25 days
C) 24 days
D) 20 days
Correct Answer: D
Solution :
(A + B)'s 1 day's work \[=\frac{1}{12}\] (B + C)'s 1 day's work \[=\frac{1}{15}\] (C + A)'s 1 day's work \[=\frac{1}{20}\] On adding, 2 (A + B + C)' s 1 day's work\[=\frac{1}{12}+\frac{1}{15}+\frac{1}{20}\] \[=\frac{5+4+3}{60}=\frac{1}{5}\] \[\therefore \] (A + B + C)'s 1 day's work \[=\frac{1}{10}\] \[\therefore \] B's 1 day's work \[=\frac{1}{10}-\frac{1}{20}=\frac{2-1}{20}=\frac{1}{20}\] \[\therefore \] B alone can do the work in 20 days.
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