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Continuous random variable (stats) 
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#1
Jun711, 01:13 PM

P: 32

The probability density function of the time customers arrive at a terminal (in minutes after 8:00 A.M) is
f(x)= (e^(x/10))/10 for 0 < x c) Determine the probability that: two or more customers arrive before 8:40 A.M among five that arrive at the terminal. Assume arrivals are independent my logic is the following: Probability= 1Probability 0 or 1 customers arrive before 8:40 A.M the answer is the following: P(X1>40)+ P(X1<40 and X2>40)= e4+(1 e4) e4= 0.0363 from what is written above, it seems to be the probability that no one arrives before 8:40 P(X1>40) and the probability that one arrives before 8:40 (X1<40) and another arrives after 8:40 (X2>40). i tihnk i just need some help on understanding why X2 is brought in. Thanks! 


#2
Jun811, 01:11 PM

P: 43

Your logic is correct. But the solution is wrong.
Let p=P(a customer arrives at the terminal before 08:40)=P(X<40)=1e^(4) Then, P(0 or 1 customers arrive at the terminal before 08:40) = (1p)^5 + nchoosek(5, 1)*p*(1p)^4 = 5.5255*10^(7) (approximately zero). Hence, P(2 or more customers arrive at the terminal before 08:40) = 15.5255*10^(7) (approximately 1) 


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