Consider the following circuit involving three D-type flip-flops used in a certain type of counter configuration.
If all the flip-flops were reset to $0$ at power on, what is the total number of distinct outputs (states) represented by $PQR$ generated by the counter?
Refer - https://gateoverflow.in/2157/gate2011-50
if we draw the state diagram from this we'll get
0 --> 2 --> 3 --> 4 --> 0
which represents a mod 4 counter, hence the total number of distinct output states = 4