We know for a n bit Ring counter , mod value is n itself..So input frequency divides with n itself..
So after going through 1st counter , we have , output frequency = Input / mod value
= Input / 25
= (2 * 106) / 25
= 80000 Hz
Now mod value of n bit ripple counter = 2n
So using 4 bit counter , we get mod value of 16..
Hence output frequency going through this counter , we have = 80000 / 16
= 5000 Hz
Now we have mod 25 counter so input frequency to it divides by 25 ,
Hence output frequency = 5000 / 25 = 200 Hz
Now we have Johnson counter finally , so mod value of n bit Johnson counter is 2n..
Hence output frequency = 200 / (2 * 4)
= 25 Hz
Hence final output frequency = 25 Hz