Answer:
By a factor of 0.1.
Step-by-step explanation:
Hello,
In this case, since the milli- unit has a factor 0.001 and the centi- unit a factor of 0.01 we can apply the following division in order to compute by what factor they actually differ from:

It means that the milli- unit differ from the centi- unit by a factor of 0.1. Conversely, the centi- unit differ from the milli- unit by a factor of 10:

Regards.