example 4.2   
when P=2, Syhchronous speed,Ns=3000 
when P=2, Syhchronous speed,Ns=1500 
when P=2, Syhchronous speed,Ns=1000 
when P=2, Syhchronous speed,Ns=750 
 
 for Nr to be 1440 , Ns will be 1500, thus p=4   
slip=4
 
 for Nr to be 940 , Ns will be 1000, thus p=6   
slip=6
 
 motor running at 940 rpm is running at higher slip