Consider the following minterm expression for F(P,Q,R,S):
F(P,Q,R,S) = sum(0, 2, 5, 7, 8, 10, 13, 15)
The minterms 2, 7, 8 and 13 are 'do not care' terms. The minimal sum-of-products form for F is
A. Q'S' + QS
B. Q'S' + QS + PQ'S + P'QS'
C. Q'S' + QRS + QR'S'
D. PR + RS + PS
GATE 2014 · Digital Logic · Min Sum of Products Form · medium
Answer: The minimal SOP is Q'S' + QS (Option A).
Fill K-map and identify groups: Place 1s at real minterms {0,5,10,15}, DC at {2,7,8,13}, 0s elsewhere. Group 1: {m0,m2,m8,m10} – all have Q=0,S=0 → PI = Q'S' (size 4). Group 2: {m5,m7,m13,m15} – all have Q=1,S=1 → PI = QS (size 4).
Verify coverage and form minimal SOP: Real minterms: m0 ∈ Q'S' ✓, m5 ∈ QS ✓, m10 ∈ Q'S' ✓, m15 ∈ QS ✓. No real minterm is missed. The expression uses only 4 literals.