Consider the following Boolean expression for \(F\): \(F(P,Q,R,S)= PQ +…

2014

Consider the following Boolean expression for \(F\):

\(F(P,Q,R,S)= PQ + \bar{P}QR + \bar{P}Q\bar{R}S\)

The minimal sum-of-products form of \(F\) is

  1. A.

    \(PQ+QR+QS\)

  2. B.

    \(P+Q+R+S\)

  3. C.

    \(\bar{P} + \bar{Q}+ \bar{R}+ \bar{S}\)

  4. D.

    \(\bar{P}R + \bar{R} \bar{P}S+P\)

Attempted by 156 students.

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Correct answer: A

Key insight: all terms contain Q, so factor Q.

  • Start: F = PQ + P'QR + P'Q R' S

  • Factor Q: F = Q(P + P'R + P'R'S)

  • Use the identity X + X'Y = X + Y with X = P and Y = R + S:

  • P + P'(R + R'S) = P + P'(R + S) = P + R + S

  • Therefore F = Q(P + R + S) = PQ + QR + QS, which is the minimal sum-of-products form.

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