A full adder circuit takes 20 ns to generate the carry-out bit and 40 ns for the sum bit. When 4, 1 bit full adders are cascaded, the maximum rate of additions per second will be $\text{____} \times 10^6 $sec. Usual Solution given The answer ... really calculate the total time taken to perform one round of four bit addition. Right? (Similar old question: https://gateoverflow.in/83500/digitals)