Consider the following minterm expression for $F$:
$$F(P,Q,R,S) = \sum 0,2,5,7,8,10,13,15$$
The minterms $2$, $7$, $8$ and $13$ are 'do not care' terms. The minimal sum-of-products form for $F$ is
- $Q \bar S+ \bar QS$
- $ \bar Q \bar S+QS$
- $ \bar Q \bar R \bar S+ \bar QR \bar S+Q \bar R S+QRS$
- $ \bar P \bar Q \bar S+ \bar P QS+PQS+P \bar Q \bar S$