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A grocery store counts the number of customers who arrive during an hour. The average over a year is 10 customers per hour. Assume the arrival of customers follows a Poisson distribution. (It usually does.) Find the probability that at least one customer arrives in a particular one minute period. Round your answer to 3 decimals. Find the probability that at least two customers arrive in a particular 4 minute period. Round your answer to four decimals.

User Norbert Radyk
by
2.6k points

1 Answer

23 votes
23 votes

Answer:

0.1535 = 15.35% probability that at least one customer arrives in a particular one minute period.

0.1443 = 14.43% probability that at least two customers arrive in a particular 4 minute period.

Explanation:

In a Poisson distribution, the probability that X represents the number of successes of a random variable is given by the following formula:


P(X = x) = (e^(-\mu)*\mu^(x))/((x)!)

In which

x is the number of sucesses

e = 2.71828 is the Euler number


\mu is the mean in the given interval.

Find the probability that at least one customer arrives in a particular one minute period.

The average is of 10 customers per hour(60 minutes), so for this case,
\mu = (10)/(60) = (1)/(6)

This is:


P(X \geq 1) = 1 - P(X = 0)

In which


P(X = x) = (e^(-\mu)*\mu^(x))/((x)!)


P(X = 0) = \frac{e^{-(1)/(6)}*((1)/(6))^(0)}{(0)!} = 0.8465


P(X \geq 1) = 1 - P(X = 0) = 1 - 0.8465 = 0.1535

0.1535 = 15.35% probability that at least one customer arrives in a particular one minute period.

Probability that at least two customers arrive in a particular 4 minute period.

The average is of 10 customers per hour(60 minutes), so for this case,
\mu = (10*4)/(60) = (4)/(6) = (2)/(3)

This probability is:


P(X \geq 2) = 1 - P(X < 2)

In which


P(X < 2) = P(X = 0) + P(X = 1)

So


P(X = x) = (e^(-\mu)*\mu^(x))/((x)!)


P(X = 0) = \frac{e^{-(2)/(3)}*((2)/(3))^(0)}{(0)!} = 0.5134


P(X = 1) = \frac{e^{-(2)/(3)}*((2)/(3))^(1)}{(1)!} = 0.3423


P(X < 2) = P(X = 0) + P(X = 1) = 0.5134 + 0.3423 = 0.8557


P(X \geq 2) = 1 - P(X < 2) = 1 - 0.8557 = 0.1443

0.1443 = 14.43% probability that at least two customers arrive in a particular 4 minute period.

User Corentin Branquet
by
3.3k points
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