b) 4 hours
c) 3 hours
d) 5 hours
Answer: a
Explanation:
(A + B + C)’s efficiency
= 3 + 2 + 1
= 6 units/hr
(A + B + C) can fill the tank in
$$\eqalign{ & {\text{ = }}\frac{{{\text{Total Capacity}}}}{{{\text{Efficiency of}}\left( {{\text{A + B + C}}} \right){\text{ }}}} \cr & = \frac{{12}}{6} \cr & = 2{\text{ hours}} \cr} $$
Join The Discussion