It is known that 60% mice inoculated with a serum are protected from a certain disease. If 5 mice are inoculated, find the probability that more than 3 contact the disease.
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Solution
Mice with serum = 0.6
Mice without serum = 0.4
4 contact disease = (0.4)4×(0.6)1×5!4!×1!
5 contact disease = (0.4)5×(0.6)0×5!5!×0!
Probability = (0.4)4(0.6×5+0.4)=3.4×(0.4)4=0.08704