To find the probability that all 4 computers with the critical file fail, we can use the concept of independent events.
The probability that a single computer with the critical file fails is 10/30, since there are 10 failed computers out of a total of 30.
Since there are 4 computers with the critical file, and we want all of them to fail, we can multiply the probabilities together:
(10/30) * (10/30) * (10/30) * (10/30) = 0.0123
Rounded to four decimal places, the probability is approximately 0.0123.