An empty tank can be filled by pipe A in 4 hours and by pipe B in 6 hours. If the two pipes are opened for 1 hour each alternately with first opening pipe A, then the tank will be filled in :
1
\(4\frac{2}{3}\) hours
2
\(3\frac{1}{4}\) hours
3
\(4\frac{1}{2}\) hours
4
\(3\frac{1}{2}\) hours