Answer:
The probability that all nine references are still good two years later is P(all nine are still good)=0.29.
The assumption we have to make is that the occurrence of the site references in the paper are independent events.
Step-by-step explanation:
The assumptions we have to make about the papers is that their probabilities of survival are independent of each other. This is the same as saying: The occurrence of the site references in the paper are independent events.
The probabilities of survival of any reference is:
The probability of the nine references are still good later can be calculated as:
The probability that all nine references are still good two years later is P=0.29.