SSC CGL 9 Aug 2015 Shift 2 Paper

Part of tank filled in first two hours
= $\frac{1}{4}+\frac{1}{6}$
= $\frac{3+2}{12}$ = $\frac{5}{12}$
Part of tank filled in first 4 hours
= $\frac{10}{12}$ = $\frac{5}{6}$
Remaining part
= 1 *- $\frac{5}{6}$ = $\frac{1}{6}$
This remaining part willl be filled by pipe A.
Time taken by pipe A
= $\frac{1}{6}$ × 4 = $\frac{2}{3}$ hour
∴ Total time
= 4 + $\frac{2}{3}$
= 4 $\frac{2}{3}$ hours