1. **Problem statement:**
We have an average rate of 150 cars per hour passing a point. We want to find probabilities related to the number of cars passing in different time intervals, assuming a Poisson process.
2. **Formula and explanation:**
The number of cars passing in a time interval follows a Poisson distribution with parameter $\lambda = \text{rate} \times \text{time}$.
The Poisson probability mass function is:
$$P(X = k) = \frac{\lambda^k e^{-\lambda}}{k!}$$
where $k$ is the number of events (cars), and $\lambda$ is the expected number of events in the interval.
3. **Calculate the rate per minute:**
Since 150 cars pass per hour, the rate per minute is:
$$\lambda_{1\text{ min}} = \frac{150}{60} = 2.5$$
cars per minute.
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**i. Probability of congestion in any one minute (more than 6 cars):**
We want $P(X > 6)$ where $X \sim \text{Poisson}(2.5)$.
Calculate:
$$P(X > 6) = 1 - P(X \leq 6) = 1 - \sum_{k=0}^6 \frac{2.5^k e^{-2.5}}{k!}$$
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**ii. Probability that from 8 to 13 cars pass in any eight-minute period:**
First, find $\lambda$ for 8 minutes:
$$\lambda_{8\text{ min}} = 2.5 \times 8 = 20$$
We want:
$$P(8 \leq X \leq 13) = \sum_{k=8}^{13} \frac{20^k e^{-20}}{k!}$$
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**iii. Probability that at most 2 cars pass in any 30-second period:**
30 seconds is 0.5 minutes, so:
$$\lambda_{0.5\text{ min}} = 2.5 \times 0.5 = 1.25$$
We want:
$$P(X \leq 2) = \sum_{k=0}^2 \frac{1.25^k e^{-1.25}}{k!}$$
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**Summary:**
- $\lambda_{1\text{ min}} = 2.5$
- $P(X > 6) = 1 - \sum_{k=0}^6 \frac{2.5^k e^{-2.5}}{k!}$
- $\lambda_{8\text{ min}} = 20$
- $P(8 \leq X \leq 13) = \sum_{k=8}^{13} \frac{20^k e^{-20}}{k!}$
- $\lambda_{0.5\text{ min}} = 1.25$
- $P(X \leq 2) = \sum_{k=0}^2 \frac{1.25^k e^{-1.25}}{k!}$
These sums can be computed using a calculator or software for exact numerical values.
Poisson Cars B659F2
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