A series DC motor has a feld coil resistance of 1.0 Ω and an armature coil resistance of 0.5 Ω. It takes a current of 20 A from a 250 V supply when running at a speed of 1000 rev/min. At what speed...

A series DC motor has a feld coil resistance of 1.0 Ω and an armature coil resistance of 0.5 Ω. It takes a current of 20 A from a 250 V supply when running at a speed of 1000 rev/min. At what speed will it run when a 3.5 Ω resistance is placed in series with the motor if the same current is taken as before?