What are two rationales for adding centerpoints to a ffe?

a: b: in a box-wilson central composite, for a 2 5−2 experiment what is α [starpoint] factor used?

a: ≈ 0.7071
b: ≈ 1.6818
c: ≈ 2.828
d: ≈ 4.000
e: ≈ 16.000
f: not possible to do a ccc design with more than 4 factors why do pb designs not have centerpoints?
a: which are valid run sizes for a single replicate of a plackett-burman design?

a: 17
b: 132
c: 8
d: 18