With reference to Exercise 4.87, find the mean and the variance of the distribution of the number of microelectrodes made from glass tubing using

(a) the probabilities obtained in that exercise;

(b) the special formulas for the mean and the variance of a hypergeometric distribution.

Data From Exercise 4.87

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4.87 In 16 experiments studying the electrical behavior of single cells, 12 use micro-electrodes made of metal and the other 4 use micro-electrodes made from glass tubing. If 2 of the experiments are to be terminated for financial reasons, and they are selected at random, what are the probabilities that (a) neither uses micro-electrodes made from glass tubing? (b) only one uses micro-electrodes made from glass tubing? (c) both use micro-electrodes made from glass tubing?