Any process will get its turn after n-1 have finished running their quantum so and there are 100 processes to be scheduled ( including the concerned process) before the concerned process starts running.
T = (n-1)*Tq + n*Ts ,
T = 1 = 99*Tq + 100*0.001/1000
99Tq = 1-0.0001 , Tq = 10.1 ms