I was composing the Karnaugh table for the expression $x'y'z'+x'y'z+x'yz'+x'yz+xy'z+xyz$.
The book has the answer:

My question is why the last row $1$'s are grouped as a double group whereas taking together above $1$'s could make a quarter and this is what we want. To make the groups as large as possible. Also groups can overlap. So what is the trick here?