A 230 V DC series motor has an armature circuit resistance of 0.2 Ω and field resistance of 0.1 Ω. At rated voltage, the motor draws a line current of 40 amps and runs at a speed of 1000 rpm. The speed of the motor for a line current of 20 A at 230 V is ______ (in rpm). Assume that the flux at 20 A line current is 60% of the flux at 40 A line current.
Enter numerical value using the virtual keypad. Round off where necessary.