A series motor runs at 600 rpm when taking 110 amps from a 230 V supply. The resistance of the armature circuit is 0.12 ohms and that of the series winding is 0.03 ohms. Calculate the speed when the current has fallen to 50 amps, assuming the useful flux per pole for 110 amps to be 0.024 Wb and that for 50 amps to be 0.0155Wb.