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Use the following information to answer the next three exercises. The Sky Train from the terminal to the rental–car and long–term parking center is supposed to arrive every eight minutes. The waiting times for the train are known to follow a uniform distribution. The probability of waiting more than seven minutes given a person has waited more than four minutes is? a. 0.125 b. 0.25 c. 0.5 d. 0.75

Short Answer

Expert verified
The probability is 0.25 (option b).

Step by step solution

01

Understand the Uniform Distribution

Waiting times follow a uniform distribution with a minimum of 0 minutes and a maximum of 8 minutes. The uniform distribution means every waiting time within this interval is equally likely.
02

Define Conditional Probability

We need to find the probability of waiting more than seven minutes given that the person has already waited more than four minutes. This is expressed as the conditional probability \( P(X > 7 | X > 4) \).
03

Calculate the Range for Conditional Probability

Given \( X > 4 \), the waiting time will be between 4 and 8 minutes. Thus, we must consider only this interval (4 to 8) when calculating our probabilities.
04

Determine Probabilities Within the Relevant Range

Within the interval from 4 to 8 minutes, calculate the probability that \( X > 7 \). Since the distribution is uniform, the length of the interval where \( X > 7 \) is from 7 to 8 minutes.
05

Calculate the Desired Probability

Calculate the probability of waiting more than 7 minutes: \[P(X > 7 | X > 4) = \frac{\text{Length of interval [7, 8]}}{\text{Length of interval [4, 8]}} = \frac{8 - 7}{8 - 4} = \frac{1}{4} = 0.25\]The probability is 0.25.

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Key Concepts

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

Uniform Distribution
In the realm of statistics, a uniform distribution represents an equal likelihood for each outcome within a defined range. When you think of waiting for a train that arrives between set time intervals, such as every 8 minutes, this can often be modeled using a uniform distribution. Simply put, no matter what specific time within that interval you check, the probability of the train arriving is the same.

Picture a straight line stretching from 0 to 8 on a number line. With a uniform distribution, there is no peak or dip—just a flat line indicating that every point along this line is just as likely to occur as any other. This method applies to situations where each outcome is equally probable, making it distinctively straightforward compared to other distributions.

In our exercise, understanding that each moment of waiting, from 0 to 8 minutes, is equally probable helps us calculate specific probabilities. Whenever you encounter scenarios like equal time intervals or unbiased rolling of a dice, think uniform distribution—simple, linear, and equal!
Probability Calculation
Probability calculation involves determining the likelihood of an event happening based on certain conditions, or even without any conditions at all. Let's break it down with the classical conditional probability example from our exercise—waiting for the train.

To find the probability that the train arrives after a certain time, given a person has already waited for some time, requires us to calculate a conditional probability. It's like filtering results based on a new condition and checking the likelihood of further possibilities.

Here's how it's done:
  • First, identify the total range of interest—in our exercise, between 4 and 8 minutes, since the passenger has already waited more than 4 minutes.
  • Next, determine the specific range within the total interval that satisfies your condition. For the train to arrive after 7 minutes, we look at the interval between 7 and 8.
  • Finally, calculate the probability using the length of these intervals: \( P(X > 7 | X > 4) = \frac{\text{Length of interval } [7, 8]}{\text{Length of interval } [4, 8]} = \frac{1}{4} = 0.25\).
Conditional probability focuses your calculations on a relevant section of the data, giving you insight into outcomes under specified conditions.
Educational Statistics
Educational statistics is a crucial field that encompasses various statistical techniques to enhance learning and decision-making processes. By incorporating statistical methods, educational statistics help in analyzing and interpreting data, making it vital for educators, students, and policymakers alike.

Our exercise provides an opportunity to learn and apply statistical concepts like uniform distribution and probability calculation—two fundamentals of the discipline. Working through such exercises prepares students to handle real-world data situations, fostering critical thinking and solidifying analytical skills.

Educational statistics does not just involve number crunching; it delivers insights, helps make informed decisions, and solves problems in educational settings. Whether determining the effectiveness of a new teaching method or predicting outcomes, understanding these statistics can lead to tangible benefits in academia and beyond. Learning these concepts with real-world examples makes the theoretical aspects more engaging and comprehensible for everyone.

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Most popular questions from this chapter

Use the following information to answer the next ten exercises. A customer service representative must spend different amounts of time with each customer to resolve various concerns. The amount of time spent with each customer can be modeled by the following distribution: \(X \sim Exp(0.2)\) State the probability density function.

Use the following information to answer the next three exercises. The Sky Train from the terminal to the rental–car and long–term parking center is supposed to arrive every eight minutes. The waiting times for the train are known to follow a uniform distribution. Find the \(30^{\text { th }}\) percentile for the waiting times (in minutes). a. two b. 2.4 c. 2.75 d. three

A web site experiences traffic during normal working hours at a rate of 12 visits per hour. Assume that the duration between visits has the exponential distribution. a. Find the probability that the duration between two successive visits to the web site is more than ten minutes. b. The top 25% of durations between visits are at least how long? c. Suppose that 20 minutes have passed since the last visit to the web site. What is the probability that the next visit will occur within the next 5 minutes? d. Find the probability that less than 7 visits occur within a one-hour period.

Use the following information to answer the next eight exercises. A distribution is given as \(X \sim U(0,12)\). What is b? What does it represent?

For each probability and percentile problem, draw the picture. A subway train on the Red Line arrives every eight minutes during rush hour. We are interested in the length of time a commuter must wait for a train to arrive. The time follows a uniform distribution. a. Define the random variable. X = _______ b. X ~ _______ c. Graph the probability distribution. d. f(x) = _______ e. ? = _______ f. ? = _______ g. Find the probability that the commuter waits less than one minute. h. Find the probability that the commuter waits between three and four minutes. i. Sixty percent of commuters wait more than how long for the train? State this in a probability question, similarly to parts g and h, draw the picture, and find the probability.

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