13.2 Within a set of papers on a particular topic it is found that the average paper cites 30 others in the set. Moreover the network of citations among the papers appears to be scale-free, with power-law exponent=3. Let us assume that the network is well described by the preferential attachment model of Price, discussed in Section 13.1. a) What is the average number of citations received by a paper? b) On average what fraction of papers receive no citations at all? c) On average what fraction of papers receive 100 or more citations? d) The set consists of 10 000 papers. What is the probability that the 100th paper published has no citations? What is the probability that the 100th-to-last paper published has no citations?