Question

Figure gives a system of logic gates. From the study of truth table it can be found that to produce a high output (1) at R, we must have

• A. X = 0, Y = 1
• B. X = 1, Y = 1
• C. X = 1, Y = 0
• D. X = 0, Y = 0

Answer 1

The correct option is C X = 1, Y = 0

The truth table can be written as
$\begin{array}{ccccccc}X& Y& \overline{X}& \overline{Y}& P=\overline{X}+Y& Q=\overline{X.\overline{Y}}& R=\overline{P+Q}\\ 0& 1& 1& 0& 1& 1& 0\\ 1& 1& 0& 0& 1& 1& 0\\ 1& 0& 0& 1& 0& 0& 1\\ 0& 0& 1& 1& 1& 1& 0\end{array}$

Hence X=1, Y=0 gives output R=1