RRB Group D Model Paper 9 with solutions

(2)
(A+B)'s 1 day's work = $\frac{1}{12}$ ,
(B+C)'s 1 day's work = $\frac{1}{15}$
and (C+A)'s 1 day's work $\frac{1}{20}$
So, 2(A+B+C)'s 1 day's work
= $\frac{1}{12}+\frac{1}{15}+\frac{1}{20}$
(A+B+C)'s 1 day's work = $\frac{12}{120}=\frac{1}{10}$ .
So, A's 1 day's work
= $\frac{1}{10}-\frac{1}{15}=\frac{1}{30}$
Therefore, A alone can complete the work in 30 days.