Because the diameter of the oil drop is 0.2CM and the diameter of the square hole is 1CM, the oil drop completely falls into the square hole, that is, the center point of the oil drop falls within 0. 1CM from the edge of the square hole. That is to say, only when the center of the oil drop is in a square area with a center and a side length of 0.9CM can the oil drop completely fall into a square hole with a side length of 1CM.

Then, the probability of this problem is the probability that the center point of the oil drop falls in a square with a side length of 0.9CM, and the ratio of the points in the square area with a side length of 0.9CM to the points in the circle is their area ratio, that is, 0.8 1/(4π).

Because the volume of oil droplets can't be ignored, the answer is definitely not 1/(4π).