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# In a book of 500 pages, it is found that there are 250 typing errors. Assume that Poisson law holds for the number of errors per page. Then, the probability that a random sample of 2 pages will contain no error, is :

$\begin {array} {1 1} (a)\;e^{-0.3} & \quad (b)\;e^{-0.5} \\ (c)\;e^{-3} & \quad (d)\;e^{-2}\end {array}$

$(c)\;e^{-3}$