Consider the following figure with three counters where MSB and LSB of counter 1 are clock inputs to counter 2 and counter 3 respectively.

Output Y = 1 when inputs a2a1a0 and b2b1b0are equal. Initially all the counters are cleared. So, initially Y=1. Eleven external clock pulses are needed to get output Y = 1 again. What is the state of counter 2 or counter 3 after eleven clock pulses?
Solution
Initial state of all the Counters is 000.
CLK 1: Counter 1 goes to state 111. Now Counter 2 and 3 update their states (to 001 and 111, respectively) because of +ve edge.
CLK 2 : Counter 1 goes to state 110.
CLK 3 : Counter 1 goes to state 101. Counter 3 updates its states because of +ve edge. New state is 110
CLK 4 : Counter 1 goes to state 100.
CLK 5 : Counter 1 goes to state 011. Counter 3 updates its states because of +ve edge. New state is 101
CLK 6 : Counter 1 goes to state 010.
CLK 7 : Counter 1 goes to state 001. Counter 3 updates its states because of +ve edge. New state is 100
CLK 8 : Counter 1 goes to state 000.
CLK 9 : Counter 1 goes to state 111. Counter 2 and 3 update their states (010 and 011, respectively)because of +ve edge.
CLK 10 : Counter 1 goes to state 110.
CLK 11 : Counter 1 goes to state 101. Counter 3 updates its states because of +ve edge. New state is 010
After 11 clock pulses the counters 2 and 3 reached the same state i.e., 010.