Four fair dice are thrown independently


Four fair dice are thrown independently 27 times. Then the expected number of times, at least two dice show up a three or a five, is______.


Probability of getting at least two 3 's or 5 's in one trial

$={ }^{4} C_{2}\left(\frac{2}{6}\right)^{2}\left(\frac{4}{6}\right)^{2}+{ }^{4} C_{3}\left(\frac{2}{6}\right)^{3}\left(\frac{4}{6}\right)+{ }^{4} C_{4}\left(\frac{2}{6}\right)^{4}$


$E(x)=n p=27\left(\frac{11}{27}\right)=11 .$

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