Students Arrive at a Health Center, According to a Poisson

Students arrive at a health center, according to a Poisson distribution, at a rate of 4 every 15 minutes. Let x represent number of students arriving in a 15 minute time period.
What is the probability that no more than 3 students arrive in a 15 minute time period?
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What is the probability that exactly 5 students arrive in a 15 minute time period?
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What is the probability that more than 5 students arrive in a 15-minute time period?
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What is the probability that between 4 and 8 students, inclusively, arrive in a 15-minute time period?
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