Math Problem Statement

The computer that controls a bank's automatic teller machine crashes a mean of 0.3 times per day. What is the probability that, in any seven-day week, the computer will crash less than 1 time? Round your answer to four decimal places.

Solution

This problem involves finding the probability of a certain number of events occurring within a fixed interval of time, which is best handled using the Poisson distribution. The Poisson distribution is used to model the number of events that occur in a fixed interval of time or space under the following conditions:

  1. The events occur independently.
  2. The average rate (mean number of events) is constant.
  3. Two events cannot occur at exactly the same time.

Given:

  • Mean number of crashes per day (λday\lambda_{day}) = 0.3
  • Number of days = 7
  • Total mean number of crashes in a week (λweek\lambda_{week}) = λday×7=0.3×7=2.1\lambda_{day} \times 7 = 0.3 \times 7 = 2.1

We need to find the probability that the computer will crash less than 1 time in a 7-day week. This corresponds to finding P(X<1)P(X < 1) where XX is a Poisson random variable with λ=2.1\lambda = 2.1.

Step 1: Calculate P(X=0)P(X = 0)

The Poisson probability mass function is given by: P(X=k)=λkeλk!P(X = k) = \frac{\lambda^k e^{-\lambda}}{k!} For k=0k = 0: P(X=0)=2.10e2.10!=e2.1P(X = 0) = \frac{2.1^0 e^{-2.1}}{0!} = e^{-2.1}

Step 2: Calculate the probability

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

Let's calculate e2.1e^{-2.1}.

The probability that the computer will crash less than 1 time in a seven-day week is 0.1225.

Would you like more details on this calculation, or do you have any further questions?

Here are five related questions you might find interesting:

  1. What is the probability that the computer crashes exactly 2 times in a week?
  2. How would the probability change if the mean number of crashes per day increased to 0.5?
  3. What is the expected number of crashes in a 30-day month?
  4. How does the Poisson distribution differ from the binomial distribution?
  5. What is the probability that the computer will crash at least once in a week?

Tip: The Poisson distribution is often used for modeling rare events over a fixed period of time or space.

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Math Problem Analysis

Mathematical Concepts

Probability
Poisson Distribution

Formulas

P(X = k) = (λ^k * e^(-λ)) / k!

Theorems

Poisson Probability Theorem

Suitable Grade Level

Grades 10-12