A 4 pole DC motor runs at 600 rpm on full load taking 25 A at 450 V. The armature is Lap wound with 500 conductors and flux per pole is expressed by the relation  \((\phi=1.7\times 10^{-2}\times I^{0.5})\)  weber, where I is the motor current.

If supply voltage and torque are both halved, the speed at which the motor will run is _________ (in rpm)