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The number of automobiles that arrive at a certain intersection per minute has a Poisson distribution with a mean of 5 . Interest centers around the time that elapses before 10 automobiles appear at the intersection. (a) What is the probability that more than 10 automobiles appear at the intersection during any given minute of time? (b) What is the probability that more than 2 minutes are required before 10 cars arrive?

Short Answer

Expert verified
The exact values will depend on the calculations made in Steps 1 and 2, which involve summation of several terms of the Poisson distribution, and it is usually done using statistical software. The steps above provide the process to perform these calculations.

Step by step solution

01

Calculating the probability for more than 10 cars in a minute

To solve for the first question, we need to utilize the Poisson distribution formula, which is \( P(x; μ) = \frac{e^{-μ} * μ^{x}}{x!}\) where x is the actual number of successes that result from the experiment, and e is approximately equal to 2.71828 (base of natural logarithms). We want the probability of more than 10 cars, which is essentially 1 minus the probability of 10 or less cars. Hence, we calculate \( P(X > 10) = 1 - P (X ≤ 10)\). This implies that we sum up the probabilities for x=0 to x=10 and subtract this from 1. It is important to note that μ = 5.
02

Calculating the probability that more than 2 minutes are needed for 10 cars to arrive

For the second part, we need to interpret '2 minutes' as '2 cars per minute'. That is, we redefine λ (lambda, the Poisson parameter) as 2*5 = 10. In this case, we want to calculate the probability P(Y ≤ 9) where Y ~Poisson(10). Since we are looking for more than 2 minutes before 10 cars arrive, it means we want to calculate the probability of 9 or fewer cars arriving in 2 minutes. Therefore we set x from 0 to 9 and perform the calculations.
03

Interpret the results

Upon finishing the calculations, the results obtained for each part of the question should be interpreted in the context of the problem. Compare these results to the given parameters of the Poisson distribution.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Probability Calculations
In dealing with odds and chances, especially when conditions involve frequent occurrences over time, probability calculations play a crucial role. When you anticipate a certain event's frequency, such as cars arriving at an intersection, the Poisson distribution is often employed. It involves calculating probabilities for different scenarios, like more than 10 cars appearing in a minute.

The calculation begins with the Poisson distribution formula: \[ P(x; μ) = \frac{e^{-μ} * μ^{x}}{x!} \]This formula finds the probability of a given number of events (x events) happening in a fixed interval of time. For our scenario,
  1. We determine 'e' as approximately 2.71828, the base of natural logarithms.
  2. The mean (μ)is the average rate of success, which is 5 car arrivals per minute.
  3. Summing up probabilities from 0 to 10 cars gives the probability of 10 or fewer cars.
  4. Subtracting this sum from 1 gives the probability of more than 10 cars.
With a clear setup, this calculation helps in probabilistically understanding practical issues like traffic flow at intersections.
Mean Arrival Rate
When analyzing the frequency of events, the mean arrival rate provides a statistical idea of how often something typically occurs. In our car arrival scenario, the mean arrival rate ( λ) is critical. It conveys the average number of occurrences within a given period.

In a Poisson context:
  • Original Context: The mean arrival rate is 5 cars per minute at the intersection.
  • Modified Context:: If considering two minutes, the mean becomes 2 multiplied by the original rate. So here, λ =10 (because 2 minutes is two times the original mean).
Understanding the mean arrival rate helps us meticulously calculate probabilities over varying intervals. In this exercise, recognizing that the original interval changes implicitly when shifting from a one-minute perspective to a two-minute context is vital.
Statistical Interpretation
After performing statistical calculations, the interpretation of results plays a key role. It links math to real-world contexts—such as predicting traffic.

For this scenario:
  • Probability of More than 10 Cars: By understanding the calculation of probability for more than 10 cars, we evaluate traffic scenarios that exceed expected flows, perhaps aiding in planning traffic management strategies.
  • Time Interval Extensions: The probability of more than 2 minutes before 10 cars arrive helps to assess situations where traffic is slower than usual. This understanding could pinpoint scenarios that may need interventions or adjustments.
Statistical interpretations require recognizing the significance of results relative to objectives—like congestion patterns at intersections. Through careful interpretation, informed decisions can be made, improving systems by anticipating behavior.

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