LIC AAO Model Paper 3

Part of the tank filled by three pipes (A + B + C) in 1 hour
= $\frac{1}{6}$
∴ Part filled in 2 hours = $\frac{2}{6}$ = $\frac{1}{3}$
Remaining part = 1 - $\frac{1}{3}$ = $\frac{2}{3}$
Part filled by (A + B) in 7hours = $\frac{2}{3}$
∴ (A + B)'s 1 hour’s work = $\frac{2}{21}$
∴ Part filled by C in 1 hour = Part filled by (A + B + C) in 1 hour - Part filled by (A + B) in 1 hour
= $\frac{1}{6}-\frac{2}{51}$ = $\frac{14-8}{84}$ = $\frac{6}{84}$ = $\frac{1}{14}$
∴ C alone can fill the tank in 14 hours