Internet sites often vanish or move, so that references to them can’t be followed. In fact, 13% of Internet sites referenced in major scientific journals are lost within two years after publication. If a paper contains seven Internet references, what is the probability that all seven are still good two years later? What specific assumptions did you make in order to calculate this probability?

Question

anonymous · Answer

The probability of a reference still being good is one minus the probability of it being lost, so 87%. Assuming that the probabilities are independent for each reference (which wouldn't be the case if there were multiple references to the same domain, for example), we simply take $.87^7$ to find the probability they are all good.

anonymous · Answer

Awesome! thank you! can you help me with this?

Choose an American and a Chinese at random, independently of each other. What is the probability that both have type O blood? What is the probability that both have the same blood type?

Blood type     O       A        B         AB

Chinese         35     27       26       12
American       45     40       11        4

anonymous · Answer

It's preferable if you open a new question so people know you have a new question :)