Question 1183518
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If calls to your cell phone are a Poisson process with a constant rate =2 calls per hour, 
what’s the probability that, if you forget to turn your phone off in a 1.5 hour movie, 
your phone rings during that time?
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From the "given" part,  we know the following:

    - The Poisson random variable is 1 (we are focused on getting at least ONE phone call).

    - The average rate of success in this particular time interval of 1.5 hours 
      is 2 phone calls multiplied by 1.5 hours, i.e.  2*1.5 = 3 phone calls per time period of 1.5 hours. 

      Here we define a "success" as the phone ringing. 
      Since the phone rings two times per hour (as average; given), the average rate of phone ringing 
      is  2*1.5 = 3 times per this particular time period of 1.5 hours.


Use free of charge online calculator of the Poisson Probability

https://stattrek.com/online-calculator/poisson.aspx


Plug those numbers into the Poisson Calculator and hit the Calculate button. 
The calculator reports that the cumulative Poisson probability is  0.95021.               <U>ANSWER</U>
That is the cumulative probability of getting at least one phone call in 1.5 hours. 
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Solved and carefully explained.