Final answer:
Without additional information on the total number of machines and the nature of their failures, it is not possible to accurately calculate the probability of exactly three specified machines failing.
Step-by-step explanation:
The question pertains to the probability of a specific event occurring, which involves multiple machines failing. Since no specific information is given regarding the total number of machines or any conditions that affect the failure of these machines, it is not possible to provide an accurate calculation or a guess for the probability. Typically, a probability question like this would require knowledge of the total number of machines and whether the failures are independent events to provide a proper calculation.