d.c.motor

Sorry I think you missed the way to your examination class, BTW this is CR4 and you are welcome here, Now can you please rephrase your Question?

The number of steps of armature resistance for starting a DC shunt motor depends on

1. Internal Armature resistance voltage drop at rated current as proportion of supply voltage.
2. maximum permitted peak armature current during starting as proportion of rated current.

If 1. is high proportion e.g. 0.15 [small motor] and 2. is big e.g. 2.5 In then 2 stages may be enough, but 3 or 4 stages or more are common if limit is 1.6 In with bigger more efficient motor.